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

GSA Special Papers
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Abstract

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 Mw5.8 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.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Subsurface geologic features of the 2011 central Virginia earthquakes revealed by airborne geophysics
Series title GSA Special Papers
DOI 10.1130/2015.2509(17)
Volume 509
Year Published 2014
Language English
Publisher Geological Society of America
Contributing office(s) Crustal Geophysics and Geochemistry Science Center
Description 9 p.
First page 509
Last page 517
Country United States
State Virginia
Online Only (Y/N) N
Additional Online Files (Y/N) N