STRUCTURAL SEISMOLOGY IN EASTERN NORTH AMERICA: RECENT RESULTS AND UPCOMING OPPORTUNITIES WITH EarthScope

The eastern margin of the continental US has an extraordinarily complex tectonic history, which encompasses two complete cycles of supercontinent assembly and breakup. The geological record of the Appalachian orogenic belt records several episodes of lithospheric accretion and continental rifting, but major questions related to its history, evolution and preservation have not yet been answered. One fundamental question relates to the pattern of mantle flow beneath the eastern US continental margin and how it has affected surface processes such as the persistence of Appalachian topography. A second fundamental question addresses how the geological architecture and topography at the surface relates to the deeper structure of the crust and lithosphere. Here we present results from the recent TEENA experiment, a deployment of 9 broadband seismometers across Virginia, West Virginia, and Ohio for 11 months in 2009-2010. Investigations of crustal structure reveal an extremely sharp transition in crustal thickness from the Piedmont to the Blue Ridge/Valley and Ridge provinces, with an increase in Moho depth of ~10 km across a distance of only ~60 km. Measurements of shear wave splitting, which contain information about seismic anisotropy and mantle flow, also exhibit a transition from mostly null (no splitting) measurements for stations located in the Piedmont and Coastal Plain, to relatively strong (~1 sec) splitting with a NE-SW fast direction for stations located in the Blue Ridge, Valley and Ridge, and Appalachian Plateau. We also discuss upcoming opportunities for collecting new geophysical observations in the eastern United States through the Transportable Array (TA) and Flexible Array (FA) components of the EarthScope USArray project.