River terrace evidence of tectonic processes in the eastern North American plate interior, South Anna River, Virginia

Journal of Geology
By: , and 

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Abstract

We show that long-recognized seismicity in the central Virginia seismic zone (CVSZ) of the eastern North American (ENAM) intraplate setting arises primarily from tectonic processes predicted by new, fully coupled plate tectonic geodynamic models. The study leverages much new geophysical and geologic data following the 2011 Mineral, VA earthquake that ruptured a steeply-dipping, NW-verging reverse fault traversed by the South Anna River. The data are primarily assembled from a flight of six fluvial terrace geomorphic markers identified and correlated on texture, relative weathering, and numeric ages including one terrestrial cosmogenic nuclide (TCN) profile and 30 luminescence dates. Terrace thickness, stratigraphic age models, and incision rates downstream and upstream of the 2011 rupture are different. Long-term river incision rates of ~25-30 m/My are superimposed on regional TCN-determined erosion rates of ~8.5 m/Myr; however, there is at least 10 m of tectonically-driven incision in the epicentral region at rates of ~30-94 m/Myr. The inferred deformation resembles a hanging wall anticline above a blind reverse fault with a diffuse overlying carapace of minor brittle faults, an interpretation supported by seismology as well as bedrock and saprolite mapped across the epicentral region. These results are further supported by channel metrics that show non-uniform channel steepness (ksn) and a predicted steady-state channel elevation different from the actual channel elevation across the epicentral region. If all of the observed deformation is a consequence of the fault that ruptured in 2011, the recurrence interval of Mineral-sized events would be ~5.5 kyrs.

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Publication type Article
Publication Subtype Journal Article
Title River terrace evidence of tectonic processes in the eastern North American plate interior, South Anna River, Virginia
Series title Journal of Geology
DOI 10.1086/712636
Edition Online First
Year Published 2021
Language English
Publisher University of Chicago Press
Contributing office(s) Crustal Geophysics and Geochemistry Science Center, Eastern Mineral and Environmental Resources Science Center, Geosciences and Environmental Change Science Center, Florence Bascom Geoscience Center
Country United States
State Virginia
Other Geospatial South Anna River
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