Skip to Main Content
Book Chapter

Subsurface geologic features of the 2011 central Virginia earthquakes revealed by airborne geophysics

By
Anjana K. Shah
Anjana K. Shah
U.S. Geological Survey, P.O. Box 25046, Denver Federal Center, MS 964, Denver, Colorado 80225, USA
Search for other works by this author on:
J. Wright Horton, Jr.
J. Wright Horton, Jr.
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
Search for other works by this author on:
William C. Burton
William C. Burton
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
Search for other works by this author on:
David B. Spears
David B. Spears
Virginia Department of Mines, Minerals, and Energy, 900 Natural Resources Drive, Suite 500, Charlottesville, Virginia 22903, USA
Search for other works by this author on:
Amy K. Gilmer
Amy K. Gilmer
Virginia Department of Mines, Minerals, and Energy, 900 Natural Resources Drive, Suite 500, Charlottesville, Virginia 22903, USA
Search for other works by this author on:
Published:
January 2015

Characterizing geologic features associated with major earthquakes provides insights into mechanisms contributing to fault slip and assists evaluation of seismic hazard. We use high-resolution airborne geophysical data combined with ground sample measurements to image subsurface geologic features associated with the 2011 moment magnitude (Mw) 5.8 central Virginia (USA) intraplate earthquake and its aftershocks. Geologic mapping and magnetic data analyses suggest that the earthquake occurred near a complex juncture of geologic contacts. These contacts also intersect a >60-km-long linear gravity gradient. Distal aftershocks occurred in tight, ~1-km-wide clusters near other obliquely oriented contacts that intersect gravity gradients, in contrast to more linearly distributed seismicity observed at other seismic zones. These data and corresponding models suggest that local density contrasts (manifested as gravity gradients) modified the nearby stress regime in a manner favoring failure. However, along those gradients seismic activity is localized near structural complexities, suggesting a significant contribution from variations in associated rock characteristics such as rheological weakness and/or rock permeability, which may be enhanced in those areas. Regional magnetic data show a broader bend in geologic structures within the Central Virginia seismic zone, suggesting that seismic activity may also be enhanced in other nearby areas with locally increased rheological weaknesses and/or rock permeability. In contrast, away from the Mw 5.8 epicenter, geophysical lineaments are nearly continuous for tens of kilometers, especially toward the northeast. Continuity of associated geologic structures probably contributed to efficient propagation of seismic energy in that direction, consistent with moderate to high levels of damage from Louisa County to Washington, D.C., and neighboring communities.

You do not currently have access to this article.
Don't already have an account? Register

Figures & Tables

Contents

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
Search for other works by this author on:
Martin C. Chapman
Martin C. Chapman
Department of Geosciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall, Blacksburg, Virginia 24061, USA
Search for other works by this author on:
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
Search for other works by this author on:
The Geological Society of America
Volume
509
ISBN print:
9780813725093
Publication date:
January 01, 2015

References

Related

A comprehensive resource of eBooks for researchers in the Earth Sciences

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

View Article Abstract & Purchase Options

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

Subscribe Now