Alps vs Apennines: “fight club” under an alluvial plane?

The Po Plain (Northern Italy) is the common foreland for two opposite verging chains: the South verging Southern Alps and the NE-verging Northern Apennines. In the central part of the plain the buried outermost thrust of the two chains face each other at less than 10 km. In recent years the Analogue Model Laboratory of the University of Pavia described and analyzed the structure and the development of the two chains (Southern Alps, Ravaglia et al., 2006 and Northern Apennines, Toscani et al., 2006 and 2009). The challenge now is to model and investigate the complex sequence of tectonic events that led to the actual setting and to check if the two opposite verging chains affect each other in some way. We analyzed a regional cross section restoring it, in order to give full details on the tectonic events sequence. Then we reproduced the evolution of the two chains in a sand-box. The apparatus was equipped with two independent backstops with opposite vergence and we moved them according with the reconstruction of the main tectonic events. Our results show that the two chains grow up independently in their first stages, but they affect each other when their outer fronts are close. In particular, with displacement measurements performed during deformation, it is evident how the Alpine outer fronts stopped the Apennines ones leading to reactivations on the internal Apennine structures.