The Southeastern United States (SEUS) preserves a detailed geologic record of the continental collision and rifting that has shaped it over billions of years. Currently the SEUS lies on a passive margin far away from ongoing tectonics, yet retains the ability to produce damaging earthquakes. It has long been suspected that the current seismicity in the SEUS is related to zones of weakness inherited from past structural boundaries; however, the mechanisms that dictate the size and location remain poorly understood and the ground shaking hazard posed by widespread sedimentary basins remains poorly quantified. P-to-S converted waves, analyzed through the receiver function technique, enable detailed imaging of lithospheric structure, but suffer from contamination in sedimented regions. Therefore, I implement a method for constraining average crustal thickness and seismic velocities while correcting for the effects of sediments. I then use high-frequency constraints on sediment structure to construct a reference velocity model for the Atlantic Coastal Plain, discussing its implications for seismic hazard. Finally, using Sp and sediment-corrected Ps receiver functions, I image the structure of the crust and mantle lithosphere across the SEUS, applying sediment corrections and identifying abrupt changes in crustal thickness that appears to be associated with active seismic zones. I discuss these structures in the context of the region’s tectonic past and future seismic hazards