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Radar images of the central Appalachian Valley and Ridge province show abrupt changes in wavelengths of folds along strike. These abrupt cross-structure terminations probably reflect lateral ramps that connect decollements at different depths. Field studies and seismic reflection surveys appear to support the radar observations. The locations of large lateral ramps may be controlled by cross-strike basement block faulting. Four large lateral ramps were identified; three of these show the shallower block to be the southwest, bringing the master decollements closer to the present ground surface in that direction. The southernmost of the lateral ramps in the central Appalachians occurs at the Roanoke reentrant where several major decollements intersect the surface.
Several smaller lateral ramps complicate the larger picture because not all of them climb section to the southwest. For example, a smaller lateral ramp just north of Mathias, West Virginia, whose westward extension may truncate the Petersburg lineament, climbs section to the northeast. Extensions of this ramp both eastward and westward from Mathias appear on the radar data as lineaments and fold discontinuities.
A large lateral ramp that climbs section toward the north is present in Highland County, Virginia. This ramp and large ramps along the Susquehanna River in Pennsylvania and at the Pennsylvania-Maryland-West Virginia border coincide with belts of igneous intrusions. Cross-strike basement block faults and lateral ramps may have represented conduits for magmas to reach the surface.
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