17-32. Advancing regional and national 3D Earth resistivity models of the United States for critical mineral resource assessments and geomagnetic hazards
The focus of research under this Opportunity is the development of 3D electrical resistivity models derived from magnetotelluric (MT) data, and the application of these models to two areas of high priority for the USGS and the Nation: 1) mapping crustal- and lithospheric-scale architecture within the context of a ‘mineral-systems’ approach to resource assessment and (2) estimation of magnetic-storm induced geoelectric fields that are hazardous for electric power grids. Presently, the development of 3D resistivity models within the U.S. is incomplete and not standardized. Research is needed into methodological aspects of model development as well as in developing novel approaches for interpreting and incorporating such models for these applications. To this end we solicit proposals touching on one or both of the following research areas:
- In response to a 2017 Presidential Executive Order, the decade-long 3D Mapping for Economic Empowerment Plan (3DEEP) will assess potential resources related to 35 critical mineral commodities essential to the U.S. economy and national security. These assessments are being carried out using a ‘mineral systems’ approach (e.g. Huston et al., 2016; McCuaig & Hronsky, 2014), in which different deposit types and various ore-forming processes are genetically linked to geodynamic and tectonic processes that leave a lasting imprint on the crust and lithosphere. A mineral-systems approach to assessment considers among other factors the geological setting, the driver of mineralization, the source and pathways for metals and fluids, and modifications post-mineralization. A major component of 3DEEP is a nationwide geophysical survey to support this effort. Both the vast land area of the U.S. and the extent of sedimentary and volcanic cover demand the use of regional- and national-scale geophysical data sets and models to define permissive tracts for critical mineral commodities. Regional 3D resistivity models have been instrumental to a mineral-system assessment in Australia and Canada, specifically in defining the tectonic/metallogenic setting and potential fluid pathways over vast areas (e.g. Robertson et al., 2016; Heinson et al., 2018). Development and improvement of such resistivity models within 3DEEP is needed to provide a 3D nationwide ‘base’ model at the mineral-system scale.
- Geomagnetic storms induce electric fields within the Earth and drive geomagnetically-induced currents (GICs) in electric transmission lines. The impact of GICs can be considerable; according to some scenarios, the future occurrence of a rare but intense magnetic storm would cause widespread failure of electric power grid operations, with deleterious impact for national security and the economy (e.g., National Research Council, 2008; National Science and Technology Council, 2015). The strength of a GIC depends on multiple factors, however, electrical resistivity structure of the Earth's subsurface is of first-order importance (Bedrosian & Love, 2015). One goal of the 2015 National Space Weather Strategy and Action Plan calls on the USGS to improve lithospheric electrical resistivity models of the United States. Initial efforts leveraging the MT component of the NSF EarthScope program have developed techniques to estimate surface geoelectric fields (e.g. Kelbert et al., 2018), to examine statistics of these fields (e.g. Love et al., 2018), and to develop regional hazard maps (Love & Bedrosian, 2018) that are important in estimating GICs. 3D resistivity models present an avenue of research that may address issues of scaling and interpolation that data-driven approaches to geoelectric field estimation suffer from.
We seek a Mendenhall Fellow to advance the development and application of regional or national-scale resistivity models. Possible topics of research include:
- Performing new and improved regional and nationwide MT inversions. How and to what extent can non-EarthScope data sets be incorporated into such inversions? How can regions without MT data be considered?
- Developing computer algorithms needed to overcome the difficulties inherent to high-resolution, continent-wide modeling.
- Analyzing existing MT data to extract additional information of value to understanding the geologic/tectonic/metallogenic framework of the nation.
- Research into the linkage(s) between deep crustal conductivity and mineral systems. What are the sources of geologically stable conductivity anomalies within the lower crust and lithospheric mantle? What do they imply about past fluid and metal transport?
- Validating existing electrical resistivity models against measured data, possibly in the context of nested multi-resolution data sets.
- Performing sensitivity analysis of geoelectric-field modeling with the goal of obtaining better constraints on the spatial and depths scales of relevance to induction hazards.
- Modeling of ground-level geoelectric fields with more realistic ionospheric current sources.
Interested applicants are strongly encouraged to contact the advisors below early in the application process to discuss project ideas.
Bedrosian, P.A. and Love, J.J. (2015) Mapping geoelectric fields during magnetic storms: Synthetic analysis of empirical United States impedances, Geophys. Res. Lett., 42 (23), 477 10,160-10,170, doi:10.1002/2015GL066636.
Heinson, G.S., Didana, Y., Soeffky, P., Thiel, S., Wise, T. (2018) The crustal geophysical signature of a world-class magmatic mineral system, Scientific Reports, 8:10608, doi:10.1038/s41598-018-29016-2.
Huston, D.L., Mernagh, T.P. Hagemann, S.G., Doublier, M.P., Fiorentini, M., Champion, D.C., Jaques, A.L., Czarnota, K., Cayley, R., Skirrow, R., Bastrakov, E. (2016) Tectono-metallogenic systems - The place of mineral systems within tectonic evolution, with an emphasis on Australian examples, Ore Geology Reviews, 76,168-210.
Kelbert, A., Bedrosian, P.A., Murphy, B. (2018) The first 3D conductivity model of the contiguous US: reflections on geologic structure and application to induction hazards, AGU book chapter, accepted.
Love, J. J., and Bedrosian, P.A. (2018) Extreme-event geoelectric hazard maps, in Extreme Space Weather: Origins, Predictability, and Consequences, edited by N. Buzulukova, chap. 9, pp. 209-230, Elsevier, Amsterdam, The Netherlands.
Love, J. J., Lucas, G.M., Kelbert, A., Bedrosian, P.A. (2018) Geoelectric hazard maps for the Mid-Atlantic United States: 100-year extreme values and the 1989 magnetic storm, Geophys. Res. Lett., 45 (1), 5-15, doi:10.1002/2017GL076042.
McCuaig, T.C. and Hronsky, J.M.A. (2014) The mineral system concept: the key to exploration targeting. Soc. Econ. Geol. Spec. Publ. 18, 153–176.
National Research Council (2008) Severe Space Weather Events: Understanding Societal and Economic Impacts: A Workshop Report. Washington, DC: The National Academies Press. doi:10.17226/12507.
National Science and Technology Council (2015) National Space Weather Action Plan, 1-38 pp., 582 Executive Office, Washington, DC.
Robertson, K., Heinson, G., Thiel, S. (2016) Lithospheric reworking at the Proterozoic–Phanerozoic transition of Australia imaged using AusLAMP Magnetotelluric data, Earth and Planetary Science Letters, 452, 27-35. doi: 10.1016/j.epsl.2016.07.036.
Proposed Duty Station: Lakewood, CO; Golden, CO.
Areas of Ph.D.: Geophysics, geology, space physics or a related field (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:
(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).
Paul Bedrosian, (303) 236-4834, firstname.lastname@example.org;
Anna Kelbert, (303) 273-8448, email@example.com;
Jeffrey Love, (303) 273-8540, firstname.lastname@example.org.
Human Resources Office Contact: Dominic Garcia, email@example.com, 303-236-9589
U.S. Department of the Interior, U.S. Geological Survey
URL: http://geology.usgs.gov/postdoc/opps/2019/17-32 Bedrosian.htm
Direct inquiries to Cara A. Campbell at firstname.lastname@example.org
Maintained by: Mendenhall Research Fellowship Program Web Team
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