Active stress map update: new breakout data in southern Apennines, Italy

Abstract

We present an updated present-day stress map of Italy focused on southern Apennines. From a tectonic point of view, the Apennines are a NE-verging thrust and fold belt characterized by a prevalent extensional tectonic regime. Indeed, along the northern front of the belt, from the Po Plain to the Adriatic offshore, compression is still active whereas it seems to be over in the southern Apennines. The latter area is well known as one of the most seismic zone in Italy, characterized by strong earthquakes in the past (M>5.5). Focal mechanisms depicts an ongoing extensional tectonic regime with T-axis about NE-SW oriented that is also evidenced by borehole breakout data, active fault patterns, and geodetic data. Within this frame, the external area of the Apenninic belt, corresponding to the foredeep and the Apulian foreland, shows a minor seismicity and a prevailing strike-slip tectonics. We have analysed 46 new deep well data (from 1300 to 5500 m depth) to better constrain the state of stress along the Apenninic belt and foredeep. Some wells are located along the Val d'Agri basin and show a prevalent NE-SW Shmin direction, quite consistent with previous results. New borehole breakouts have been interpreted in comparison to earthquake data and shallow stress regime indicators. Then, a finite-element model of the Italian region has been built, using a thin-shell finite-element code. The model predicts long-term anelastic horizontal velocities, vertically integrated stresses, and fault slip rates. The misfit between model predictions and data has been evaluated and analysed.