A comparison of structural data and seismic images for low-angle normal faults in the Northern Apennines (Central Italy): constraints on activity

\ During the past 18 Ma extensional tectonism has migrated from the Tyrrhenian sea eastward into the Northern Apennines of Italy. The extension is due in part to low-angle east-dipping normal faults, that are now exhumed in the Tyrrhenian islands and Tuscany, while additional extension is still occurring in the Apennine chain (Umbria region, c. 200 m eastward). This tectonic framework is an example where active extensional processes affecting the Umbria region can be studied in exhumed faults that are no longer active. Here a comparison between the Zuccale Fault (ZF), cropping out in the Isle of Elba, and the Altotiberina Fault (ATF), revealed by geophysical data, seismology and seismic profiles crossing the Umbria region, provide insights into the processes affecting low-angle normal fault development and evolution. Recorded microscismicity suggests that the ATF is presently active under a vertical a,. Structural analysis of the ZF depict a comparable scenario with fluid involvement during the activity. The comparison of these two structures suggests movements with fluid involvement along gently dipping planes under a vertical sigma(1), implying that these faults are mechanically weak.