STRUCTURE OF THE CRUST AND MANTLE LITHOSPHERE BENEATH THE CENTRAL APPALACHIANS: RESULTS FROM THE MAGIC EXPERIMENT (Invited Presentation)

The eastern North American margin (ENAM) is a passive continental margin that has been modified by multiple episodes of orogenesis and rifting through two complete cycles of supercontinent assembly and breakup over the past ~1.3 Ga of Earth history. It is unclear to what extent deep structures in the crust and mantle lithosphere have persisted or been modified over this timeframe, and what role deep structures beneath ENAM may play in controlling intraplate seismicity. The Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) project deployed a linear array of 28 broadband seismometers across the central Appalachian Mountains as part of the EarthScope USArray Flexible Array to study the deep structure of the ENAM margin, including beneath the Central Virginia Seismic Zone. Analysis of P-to-S and S-to-P converted seismic waves reveals evidence for significant variability in crustal and lithospheric structure across the array. Specifically, we image a sharp increase in the depth of the Moho beneath the eastern Piedmont and Valley and Ridge provinces, near the location of the central Virginia seismic zone and the epicenter of the 2011 Mineral, VA earthquake. Our results suggest that the Appalachian Mountains are overcompensated isostatically, suggesting that the lower crust is denser and stronger than typical continental crust and may have undergone incremental mineralogical changes after orogenesis. Our investigations of lithospheric thickness reveal relatively thin lithosphere beneath the Appalachian Mountains, suggesting that lithosphere has been removed; this is consistent with previous suggestions of lithospheric loss leading to upwelling, decompression melting, and surface volcanism during the Eocene. Investigations of upper mantle seismic anisotropy using SKS splitting analysis reveals sharp lateral changes in anisotropic structure across the array, consistent with changes in lithospheric anisotropy reflecting past episodes of tectonic deformation.