Reactivation of deep faults beneath Southern Apennines:evidence from the 1990–1991 Potenza seismic sequences

Abstract

We relocate the 1990–1991 Potenza (Southern Apennines belt, Italy) sequences and calculate focal mechanisms. This seismicity clusters along an E–W, dextral strike–slip structure. Secondorder clusters are also present and reflect the activation of minor shears. The depth distribution of earthquakes evidences a peak between 14 and 20 km, within the basement of the subducting Apulian plate. The analysed seismicity does not mirror that of Southern Apennines, which include NW–SE striking normal faults and earthquakes concentrated within the first 15 km of the crust. We suggest that the E–W faults affecting the foreland region of Apennine propagate up to 25 km of depth. The Potenza earthquakes reflect the reactivation of a deep, preexisting fault system. We conclude that the seismotectonic setting of Apennines is characterized by NW–SE normal faults affecting the upper 15 km of the crust, and by E– W deeper strike–slip faults cutting the crystalline basement of the chain.