17. Seismic Hazard Investigations and Quaternary Geochronology in the Inter-Mountain West
The Basin and Range province is the most active region of extension in the U.S. and is expanding in a northwestward direction at a rate of 10-11 mm/yr. GPS data acquired during the past decade document the present-day spatial distribution and characteristics of Basin and Range deformation. In some cases, these geodetic signals reveal perplexing and unexplained deformation patterns that are inconsistent with geologic expectations, such as surprisingly high extension rates along parts of the Wasatch fault zone and continued extension in the Central Nevada seismic belt. For seismic hazard analysis, it is important to reconcile the apparent discrepancy between the short-term distribution of strain as determined from geodesy and the longer-term distribution of deformation as determined from late Quaternary faulting. This research opportunity focuses on developing a better understanding of the long-term behavior of potentially seismogenic faults in the province through an improved knowledge of the regional Quaternary stratigraphic framework. We seek a postdoctoral scientist who can apply cosmogenic-nuclide surface-exposure dating to determine the age of major geomorphic elements of Basin and Range landscapes. Information about the age of these landscape elements will allow us to learn more about landscape evolution and will substantially expand the temporal record of Basin and Range paleoearthquakes, earthquake recurrence intervals, and fault slip rates. Such paleoseismic data are crucial to understanding the characteristics of fault behavior on geologically significant time scales and to accurately assessing the region's seismic hazards.
Most of the Quaternary age control in the Basin and Range province is based on correlating deposits to late Pleistocene lakes (Lahontan and Bonneville), on tectonic geomorphology, and on comparing the topographic position of deposits in the landscape. Material for radiocarbon dating is generally sparse in this arid region, and although locally very useful, luminescence dating is mostly applicable for dating eolian deposits. A crucial gap exists in establishing a Quaternary stratigraphic and geomorphic framework in the Basin and Range because of limitations in dating deposits in the age range of 30 ka to 140 ka. Much of this time span is beyond the practical limits of radiocarbon dating, but covers a time span that encompasses several earthquake (seismic) cycles for typical Basin and Range faults. Fortunately, newly evolving techniques of cosmogenic-nuclide dating of in-situ produced 26Al, 10Be, and/or 36Cl allows for the accurate dating of alluvial and colluvial deposits of middle and late Quaternary age, which is the time frame most relevant to the region's seismic hazards. Application of these techniques to fault activity studies will allow the incumbent to establish a well-founded stratigraphic framework that can be used to compare short-term (GPS) and long-term (geologic) slip histories and to judge if the contemporary or the late Quaternary deformation rates realistically define the fault's modern behavior.
Proposed Duty Station: Golden, CO
Areas of Ph.D.: Geochronology with emphasis in cosmogenic-nuclide dating, Quaternary geology and geomorphology, paleoseismology, earthquake geology
Qualifications: Applicants must meet one of the following qualifications: 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 Personnel specialist.)
Research Advisor(s): Anthony Crone, (303) 273-8591, crone@usgs.gov; Michael Machette, (303) 273-8612, machette@usgs.gov; Stephen Personius, (303) 273-8611, personius@usgs.gov
Personnel Office contact: Kathleen Scheich, (303) 236-9581, kscheich@usgs.gov
U.S. Department of the Interior, U.S. Geological Survey
URL: http://geology.usgs.gov/postdoc/2006/opps/opp17.html
Direct inquiries to Rama K. Kotra at rkotra@usgs.gov
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