Driving mechanism of tectonic activity in the northern Apennines: quantitative insights from numerical modelling

It is shown, by numerical modeling, that the recent deformation pattern observed in the northern Apennines, mainly characterized by progressive eastward migration and bowing of the belt, thrusting activity along its external front, and tensional tectonics in the internal area, can be reproduced, at a first approximation, by applying a belt-parallel (SE-NW) compression to the chain, which is simulated as a structural system characterized by a high mechanical strength and decoupled from the surrounding zones. The above compressional regime, obtained by imposing kinematic boundary conditions to the model, causes the outward escape of crustal wedges from the chain, in particular the northeastward displacement of the Romagna-Marche-Umbria Units and the counterclockwise rotation and northwestward displacement of the Ligurian Units. This kinematics produces compressional to transcompressional strain along the external front of the chain and tensional to transtensional strain in the internal area, in line with the observed features that concern both strain style and orientation of principal strains. Evidence and arguments supporting the kinematic boundary conditions and the model parameterization adopted in modeling are discussed. Numerical experiments have also been carried out to evaluate the influence of major features of the model parameterization and boundary conditions we have adopted in modeling and to provide insights into the possible influence of strong decoupling earthquakes in the central Apennines on tectonic and seismic activity in the northern Apennines. Copyright 2004 by the American Geophysical Union.