Seismic evidence of longitudinal extension in the Southern Apennines chain (Italy): The 1997-1998 Sannio-Matese seismic sequence

Abstract

We present evidence of longitudinal extension in the Apennines based on data from the 1997-1998 Sannio-Matese seismic sequence. The earthquakes occurred between the NW-SE faults responsible for larger historical earthquakes. Inversion of focal mechanisms indicates a stress field with a prevailing normal stress characterized by a NNW-SSE sub-horizontal σ3. This stress regime is consistent with normal movements along NE-SW faults. These features suggest that the NE-SW faults located in between the NW-SE faults cannot be interpreted as transfer faults or old faults reactivated during the eastward migration of the chain. We propose that the deformation due to the eastward chain migration concentrates along NW-SE normal faults, which are responsible for the largest earthquakes, whereas the deformation related to the chain curvature concentrates along NE-SW normal faults, which are responsible for the lower energy seismic sequences.