Interpretation of seismic data from the central Appalachians Valley and Ridge province reveals that a large blind thrust, the Broad Top thrust, is much more extensive than previously realized. This thrust sheet extends across the 15 mi (24 km) width of the Nittany anticlinorium, a dominate structural element that lies along the western margin of the Valley and Ridge province adjacent to the Plateau province in the Appalachian foreland. It extends for a distance along strike of at least 100 mi (160 km), and duplicates a 7800 ft (2380 m) thick sequence of Cambrian and Ordovician limestone and dolomite referred to as the Cambrian-Ordovician lithotectonic unit.

Thinning of the duplicated Cambrian-Ordovician sequence along the length of the Nittany anticlinorium by as much as 2500 ft (760 m) observed on seismic lines is attributed to removal of less brittle intervals from the base of the upper sheet and top of the lower sheet. The missing section from this inter-sheet detachment zone may have been transported toward the foreland and incorporated into the leading parts of the thrust sheet. The tectonic thinning solves space problems associated with duplication of the lithotectonic unit beneath what have previously been considered abnormally deep synclines of the anticlinorium. The abnormal depth of these synclines occurs where tectonic thinning is located on the seismic lines.

Structural traps in a triangle zone along the Allegheny structural front have been attributed to the intense shortening associated with emplacement of the Broad Top thrust sheet. The presence of the thrust sheet along the length of the structural front in West Virginia and Virginia enhances the probability of successful exploration for triangle zone structures along the entire length of the structural front. Structures produced by variable tectonic thinning in the inter-sheet detachment zone may also produce additional traps within the anticlinorium in the form of closure or associated fracture systems.