How and why the present tectonic setting in the Apennine belt has developed

The building of the Apennine belt slowed down or ceased around the Early Pleistocene. Since then, the belt has undergone strong uplift and considerable distortion. This change, from belt-normal to belt-parallel shortening, has been determined by the fact that the continental Adriatic domain (Adria) was almost completely surrounded by buoyant orogenic structures. In that context, the mobility of Adria underwent a considerable reduction, whereas uplift and deformation of its southern part was strongly emphasized as an effect of the convergence of the confining plates. Around the middle Pleistocene, the deformation pattern in the peri-Adriatic zones changed again, in response to acceleration of Adria. The outer (Adriatic) sector of the Apennine belt underwent belt-parallel shortening, accommodated by uplift and outward escape of upper crustal wedges. The separation between the extruding wedges and the almost stable inner belt has generated a series of extensional or transtensional fault systems along the axial part of the Apennines, which now correspond to the main seismogenic sources. The spatio-temporal distribution of major tectonic events in the study area can plausibly be explained as an effect of the least-action principle.