Coulomb stress transfer and modeled permanent vertical surface deformation from the August 2011, Mineral, Virginia, earthquake

Abstract

Occurring only 13 months apart, the moment magnitude, Mw 3.4 Germantown, Maryland (16 July 2010), and Mw 5.8 Mineral, Virginia (23 August 2011), earthquakes rocked the U.S. national capital region, drawing renewed attention to the occurrence of intraplate seismicity in the Mid-Atlantic region of the eastern United States. We model the Coulomb stress transferred by these earthquakes to fault zones in the Mid-Atlantic region that were active during the Cenozoic. In most cases, the Mineral earthquake brought these preexisting Cenozoic faults further from failure. This unloading, like all changes in stress located more than 30 km from the epicenter, was very small (~1–3 mbar) and therefore unlikely to affect the occurrence of earthquakes at the regional scale. Between 30 and 15 km away, however, the maximum Coulomb failure stress change ranged one to three orders of magnitude greater (~0.05–6 bar), levels on par with the stress changes that triggered historical earthquakes in California. The Mineral earthquake generated an increase in Coulomb failure stress of ~0.5 bar 10 km from the rupture, ~5 bar 5 km from the rupture, and ~20 bar at the edge of the rupture on receiver faults oriented like the mainshock. The geographic location of the aftershock-defined Northwest fault in the epicentral region may be explained by Coulomb stress transfer from the mainshock. Elastic dislocation modeling of surface deformation caused by the Mineral earthquake indicates a maximum of ~7 cm of permanent vertical surface displacement directly above the center of the rupture.