The tectonics of intraplate regions: Quantifying stress and surface deformation in the central and eastern U.S. and planetary analogs on Mercury and the Moon
Walsh, Lisa Schleicher
Martin, Aaron J
Montesi, Laurent G.J.
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Occurring ~ 1 year apart, the magnitude 3.4 Germantown, Maryland, (16 July 2010) and magnitude 5.8 Mineral, Virginia, (23 August 2011) earthquakes rocked the U.S. national capital region, drawing renewed attention to the occurrence of seismicity within continental interiors. While the majority of earthquakes concentrate at tectonic plate boundaries, the processes that promote spatially diffuse zones of seismicity in intraplate regions are not well understood. The Mineral earthquake was one of the largest earthquakes to occur east of the Rocky Mountains in the past century and offers a rare opportunity to examine the role of stress transfer, long-distance triggering, and aftershock decay within an intraplate region. Stress transfer from the Mineral and Germantown earthquakes relieved stress on the majority of Cenozoic faults in the Mid-Atlantic region, moving these faults further away from future failure. The Everona fault and southern portion of the Mountain Run fault zone were the only locations (except in the aftershock region) that were loaded from the Mineral earthquake, although by only ~1 mbar. Accumulation of stress over time is required in order to significantly affect regional seismicity. There is no evidence of remote triggering due to the passage of seismic waves in any of the major seismic zones in the central and eastern U.S. However, the slow decay rate of aftershocks suggests seismicity in the epicentral region might continue for a decade or longer. Aftershocks triggered by stress imparted by the mainshock imply that Coulomb stress transfer plays an important role in earthquake triggering processes within intraplate regions. Processes in the aftershock zone likely have the greatest influence on seismic hazard. New imagery and altimetry data returned from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and Lunar Reconnaissance Orbiter (LRO) spacecraft provide new insight into processes driving intraplate tectonic deformation. Mercurian wrinkle ridges are ~2.2 larger in mean relief than wrinkle ridges on the Moon, suggesting a larger component of global contraction on Mercury. Patterns of faulting on Mercury and the Moon, as well as in the central and eastern U.S., indicate that intraplate seismicity can concentrate in zones of pre-existing weakness and spatially migrate.