Structural studies carried out in the Lucanian Apennines (Southern Italy) show that strike-slip faulting was the principal mode of deformation of this area during middle-upper Pleistocene time. W-NW to E-SE trending left strike-slip fault systems dissect the entire Apennine mountain belt and affect the preexisting thrust geometry. Strike-slip faults, activated by a roughly E-W shortening, are characterized by different geometries representing the surface response to lateral motion occurring along deep-seated structures. The occurrence of different structural patterns which characterize different segments of strike-slip system is related to (1) the depth of a major decoupling surface which separates the upper tectonic multilayered horizon (Apennines, thrust belt system) from the lower rigid horizon (Apulian belt) in which strike-slip structures have originated and (2) the geometric relationships between the strike-slip faults and the thrust belt pattern which characterize the upper horizon. The different segments of the strike-slip system are interpreted as internal deformation developed within a crustal shear zone. This zone which corresponds to the boundary between the Apulian block and the Apennine chain, is characterized by sinistral movement as a response to the northwesterly convergent motion of the African plate with respect to Europe. ¿ American Geophysical Union 1993