A MODEL FOR THE INTRAPLATE DYNAMICS OF CENTRAL AND EASTERN NORTH AMERICA

Central and eastern North America have experienced large (M>7.0) intraplate earthquakes. The recent 2011 Mineral, Virginia M=5.8 earthquake is a reminder that intraplate stresses continue to produce events of permanent strain within the plate interior of North America. Yet, at present there is no comprehensive model to explain plate interior stresses, strains and seismicity. Although there is agreement that some of these earthquakes occur along favorably oriented ancient rifts and other major strength contrasts, there is no consensus on the sources of intraplate deformation and earthquakes. Proposed models include glacial isostatic adjustment (GIA), ridge push effects, and large-scale mantle convection. Recent studies have also argued that vertical dynamics impact the passive margin of eastern North America. We present a self-consistent model of the dynamics of eastern North America that explains the stress field responsible for these intraplate earthquakes. The earthquakes represent slow, ongoing deformation associated with forces arising from a combination of lithosphere topography and structure, coupled together with the effects of density-driven mantle flow. We show further evidence that the ancient suture between Laurentia and accreted Appalachian terranes constitutes a major strength discontinuity that explains the change in orientation of principal axes of stress along the passive margin of North America. Maximum predicted shortening rates of < 0.5 mm/yr across the Piedmont and Coastal Plane regions pose an ongoing seismic hazard. Although the large-scale driving mechanisms for intraplate deformation in eastern North America are now well defined, further work is needed to investigate the importance of other lateral strength contrasts, the magnitude of these contrasts, along with the implications for expected long-term permanent deformation and seismic moment release. Further work is also needed to fully incorporate new constraints on crustal and upper mantle structure provided by EarthScope USArray studies.