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Crustal Thickness Variations across the Blue Ridge Mountains, Southern Appalachians: An Alternative Procedure for Migrating Wide-Angle Reflection Data

Department of Geology, University of Georgia, Athens, Georgia 30602

Migration of wide-angle reflections generated by quarry blasts suggests that crustal thickness increases from 38 km beneath the Carolina Terrane to 47–51 km along the southeastern flank of the Blue Ridge. The migration algorithm, developed for generating single-fold images from explosions and earthquakes recorded with isolated, short-aperture arrays, uses the localized slant stack as an intermediate data set. In contrast with other methods, it includes an interpretive step that is based on the assumption that all coherent P-wave energy consists of reflections from planar interfaces. Each sample in the slant stack is mapped into a planar, dipping segment with a length that is determined by the recording aperture. Migrated sections from within the Blue Ridge show increases in reflectivity at depths of 20 and 40 km. High apparent reflectivity from 40 to 50–55 km suggests a layered zone in the lower crust that is similar to models proposed for the Cumberland Plateau in Tennessee and the Adirondacks. The migration results are consistent with regional gravity data and with the occurrence of crustal roots beneath the Urals, another Paleozoic orogen.