ASSOCIATION OF MODERN SEISMICITY WITH PALEOZOIC CROSS-STRIKE STRUCTURES IN THE CENTRAL VIRGINIA SEISMIC ZONE

SPEARS, David B., Virginia Department of Mines, Minerals and Energy, Division of Geology and Mineral Resources, 900 Natural Resources Drive, Suite 500, Charlottesville, VA 22903, CHAPMAN, Martin C., Department of Geosciences, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061 and WITT, Anne C., Virginia Department of Mines Minerals and Energy, Division of Geology and Mineral Resources, 900 Natural Resources Drive, Suite 500, Charlottesville, VA 22903, David.Spears@dmme.virginia.gov

Historic earthquakes in the Central Virginia Seismic Zone form clusters near cross-strike structures. We compare epicenters located by the Virginia Tech Seismological Observatory to geologic mapping by the Virginia Division of Geology and Mineral Resources and U.S. Geological Survey. Some earthquake clusters are associated with folds and faults oriented at high angles to regional strike. Focal mechanisms of earthquakes in these areas exhibit strong variability, with both along-strike and across-strike components.

The Mw 5.8 August 2011 Mineral VA earthquake and its aftershocks form a cluster in an area where local strike in deformed metamorphic rocks of the Chopawamsic and Quantico formations deviates from regional strike by 45 degrees. This deviation is defined by axial traces of open folds associated with the truncation of a splay of the Columbia-Quantico Syncline by a cross-strike reverse fault. These structures suggest the presence of a deeper cross-strike structure, possibly a lateral ramp within the Chopawamsic Formation.

A cluster of historic earthquakes along the James River near Columbia, 25 km southwest of the epicenter of the Mineral earthquake, is associated with the southwestward terminus of the main Columbia-Quantico Syncline in a second-generation fold set that folds the axial traces of first-generation folds into orientations locally perpendicular to regional strike. Near the earthquake cluster, the second-generation fold axes plunge northeast at 30 degrees, but flatten to the northeast and southwest, again indicating the presence of a deeper cross-strike structure.

Other clusters occur near Diana Mills, 25 km west of Columbia, where the Hardware Anticline plunges northeast, and near Goochland, 20 km east of Columbia, where possible cross-strike structures have been tentatively identified in regional mapping.

Although the spatial association of earthquake clusters with cross-strike structures does not necessarily indicate causality, we speculate that remnant stress from Paleozoic non-coaxial deformation may contribute to modern seismicity.

Session No. 3

T7. Lessons Learned from the 2011 Virginia Earthquake

Thursday, 10 April 2014: 8:00 AM-12:00 PM

Assembly Hall (Inn and Conference Center at Virginia Tech)

Geological Society of America Abstracts with Programs. Vol. 46, No. 3, p.5

© Copyright 2014 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.

Back to: T7. Lessons Learned from the 2011 Virginia Earthquake

<< Previous Abstract | Next Abstract

Southeastern Section - 63rd Annual Meeting (10–11 April 2014)

ASSOCIATION OF MODERN SEISMICITY WITH PALEOZOIC CROSS-STRIKE STRUCTURES IN THE CENTRAL VIRGINIA SEISMIC ZONE