The central and southern part of the Apennines has been characterised by extensional tectonics since the Pliocene epoch (i.e. about the last five million years), with most of the active faults being normal in type and NW-SE trending. The extension is due to the back-arc basin in the Tyrrhenian Sea opening faster than the African Plate is colliding with the Eurasian Plate. To the northeast of the Apennine chain, the foreland is in contrast affected by W-E trending strike-slip to oblique-slip faults.