NOT SO STABLE AFTER ALL: LITHOSPHERIC STRUCTURES BENEATH THE SOUTHEASTERN UNITED STATES (Invited Presentation)

The central and eastern United States are the product of repeated Wilson cycles over the past 1Ga, the last of which ended some 180 Ma. However, despite the intraplate setting, there is a growing body of evidence for significant tectonic activity since that time, including volcanism, deformation (e.g. uplift in the southern Appalachians and the formation of the Cape Fear Arch), and significant seismicity. The ongoing presence of seismicity, together with observed variability in the spatial distribution of these earthquakes, suggests possible lithospheric scale structural contributions to this intraplate tectonism.

Recent broadband deployments such as the South Eastern Suture of the Appalachian Margin Experiment (SESAME), together with data from the EarthScope Transportable Array, have allowed for an unprecedented look at the structures of the crust and mantle lithosphere in the upper mantle beneath the central and eastern United States. Our recent regional scale teleseismic body wave tomography study indicates that the “stable” continental interior is affected by past and ongoing episodes of lithospheric foundering. The patterns observed in mantle lithospheric structures correlate in some areas with regions of comparatively recent tectonic activity and ongoing seismicity. Results from our analyses of Rayleigh wave phase velocities and azimuthal anisotropy provide greater depth constraints to these structures, and shed light on the resultant complexities in mantle flow. Questions remain about why the lithosphere continues to evolve despite its distance from active plate boundaries, and the mechanism by which these structures may be linked to the genesis of intraplate seismicity.