River Terrace Evidence of Tectonic Processes in the Eastern North  American Plate Interior, South Anna River, Virginia

Counts, R.; Willenbring, J.; Germanoski, Dru; Malenda, H. F.; Berti, C.; Mahan, S.; Pazzaglia, F. J.; Holt, W. D.; Carter, M. W.; McGavick, M. L.; Raup, C.; Rittenour, T. M.; Nelson, M.; Peters, S. C.

River Terrace Evidence of Tectonic Processes in the Eastern North American Plate Interior, South Anna River, Virginia

Abstract

We show that long-recognized seismicity in the central Virginia seismic zone of the eastern North American 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, Virginia, earthquake that ruptured a steeply dipping, northwest-verging reverse fault traversed by the South Anna River. The data are primarily assembled from aflight of sixfluvial terrace geomorphicmarkers identified and correlated on texture, relativeweathering, andnumeric 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 similar to 25-30 m/My are superimposed on regional TCN-determined erosion rates of similar to 8.5m/My; however, there are at least 10m of tectonically driven incision in the epicentral region at rates of similar to 30-94 m/My. The inferred deformation resembles a hangingwall anticline above a blind reverse fault with a diffuse overlying carapace ofminor 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 shownonuniform channel steepness (k(sn)) 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 similar to 5.5 ky.

Title	River Terrace Evidence of Tectonic Processes in the Eastern North American Plate Interior, South Anna River, Virginia
Creator	Counts, R.
	Willenbring, J.
	Germanoski, Dru
	Malenda, H. F.
	Berti, C.
	Mahan, S.
	Pazzaglia, F. J.
	Holt, W. D.
	Carter, M. W.
	McGavick, M. L.
	Raup, C.
	Rittenour, T. M.
	Nelson, M.
	Peters, S. C.
Publisher	Journal of Geology
Academic Department	Geology & Environmental Geosciences
Division	Natural Sciences
Organization	Lafayette College
Date Issued	September 2021
Date Available	2023-04-04
Type	Article
Language	English
Bibliographic Citation	Pazzaglia, F. J., et al. (2021 Sept) "River Terrace Evidence of Tectonic Processes in the Eastern North American Plate Interior, South Anna River, Virginia." Journal of Geology 129 (5): 595-624.
Standard Identifier	Handle 10385/6m311q789
Standard Identifier	DOI 10.1086/712636
Permalink	http://hdl.handle.net/10385/6m311q789
Rights Statement	In Copyright
Rights Holders	University of Chicago