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Geologic framework and evidence for neotectonism in the epicentral area of the 2011 Mineral, Virginia, earthquake

By
William C. Burton
William C. Burton
U.S. Geological Survey, MS 926A, National Center, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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Richard W. Harrison
Richard W. Harrison
U.S. Geological Survey, MS 926A, National Center, 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, 900 Natural Resources Drive, Charlottesville, Virginia 22903, USA
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Nicholas H. Evans
Nicholas H. Evans
Virginia Department of Mines, Minerals, and Energy, 900 Natural Resources Drive, Charlottesville, Virginia 22903, USA
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Shannon Mahan
Shannon Mahan
U.S. Geological Survey, MS 974, Federal Center, Lakewood, Colorado 80225, USA
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Published:
January 01, 2015

The epicenters of the main shock and associated aftershocks of the 2011 moment magnitude, Mw 5.8 Mineral, Virginia (USA), earthquake, and the updip projection of the possible fault plane that triggered the quakes, are contained in the areas of 2 adjoining 7.5′ quadrangles in the central Virginia Piedmont. These quadrangles have therefore been the focus of concentrated geologic study in the form of bedrock and surficial mapping and near-surface trenching in order to identify potential seismogenic structures. Bedrock mapping has outlined a series of northeast-southwest–trending lithologic belts that include the Ordovician Chopawamsic and Quantico Formations, the narrow neck of the Late Ordovician Ellisville pluton, and mélange zone III of the Mine Run Complex. The region was affected by at least two ductile deformational events, one in the early Paleozoic that was broadly synchronous with the intrusion of the pluton, and one later in the Paleozoic. The earlier deformation produced the Quantico synclinorium and other regional folds, and the later deformation produced faults with associated high-strain zones. Two of these faults have been trenched at their intersection along the east-dipping eastern contact of the Ellisville neck, near where the causative fault for the earthquake projects to the surface. The trenches have exposed abundant evidence of post-Paleozoic fracturing and faulting, including brecciated quartz-tourmaline veins, slickensided thrust and strike-slip faults, and clay-filled fractures. Fluvial and colluvial gravels that overlie these brittle structures have yielded optically stimulated luminescence ages ranging from ca. 27 to 10 ka. These structures are likely representative of surface features associated with Quaternary earthquakes in the Central Virginia seismic zone.

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GSA Special Papers

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

Geological Society of America
ISBN print:
9780813725093
Publication date:
January 01, 2015

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