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The 2011 Virginia Mw 5.8 earthquake: Insights from seismic reflection imaging into the influence of older structures on eastern U.S. seismicity

By
Thomas L. Pratt
Thomas L. Pratt
U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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J. Wright Horton, Jr.
J. Wright Horton, Jr.
U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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David B. Spears
David B. Spears
Virginia Department of Mines, Minerals and Energy, Division of Geology and Mineral Resources, 900 Natural Resources Drive, Suite 500, Charlottesville, Virginia 22903, USA
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Amy K. Gilmer
Amy K. Gilmer
Virginia Department of Mines, Minerals and Energy, Division of Geology and Mineral Resources, 900 Natural Resources Drive, Suite 500, Charlottesville, Virginia 22903, USA
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Daniel E. McNamara
Daniel E. McNamara
U.S. Geological Survey, Geologic Hazards Science Center, 1711 Illinois St., Golden, Colorado 80401, USA
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Published:
January 01, 2015

The Mineral, Virginia (USA), earthquake of 23 August 2011 occurred at 6–8 km depth within the allochthonous terranes of the Appalachian Piedmont Province, rupturing an ~N36°E striking reverse fault dipping ~50° southeast. This study used the Interstate Highway 64 seismic reflection profile acquired ~6 km southwest of the hypocenter to examine the structural setting of the earthquake. The profile shows that the 2011 earthquake and its aftershocks are almost entirely within the early Paleozoic Chopawamsic volcanic arc terrane, which is bounded by listric thrust faults dipping 30°–40° southeast that sole out into an ~2-km-thick, strongly reflective zone at 7–12 km depth. Reflectors above and below the southward projection of the 2011 earthquake focal plane do not show evidence for large displacement, and the updip projection of the fault plane does not match either the location or trend of a previously mapped fault or lithologic boundary. The 2011 earthquake thus does not appear to be a simple reactivation of a known Paleozoic thrust fault or a major Mesozoic rift basin-boundary fault. The fault that ruptured appears to be a new fault, a fault with only minor displacement, or to not extend the ~3 km from the aftershock zone to the seismic profile. Although the Paleozoic structures appear to influence the general distribution of seismicity in the area, Central Virginia seismic zone earthquakes have yet to be tied directly to specific fault systems mapped at the surface or imaged on seismic profiles.

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GSA Special Papers

The 2011 Mineral, Virginia, Earthquake, and Its Significance for Seismic Hazards in Eastern North America

J. Wright Horton, Jr.
J. Wright Horton, Jr.
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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Martin C. Chapman
Martin C. Chapman
Department of Geosciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall, Blacksburg, Virginia 24061, USA
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Russell A. Green
Russell A. Green
Department of Civil and Environmental Engineering (MC 0105), 120B Patton Hall, Virginia Polytechnic Institute and State University, 750 Drillfield Drive, Blacksburg, Virginia 24061, USA
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The Geological Society of America
Volume
509
ISBN print:
9780813725093
Publication date:
January 01, 2015

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