Seismicity and stress field in the Sannio-Matese area

Abstract

In this study we discuss the available data on seismicity and focal mechanisms in the Sannio-Matese area in order to obtain information on the stress field acting in the area. Background seismicity of the area is characterized by isolated events, with magnitude generally less than 2.5, on which is superimposed a swarm and seismic sequence activity of low magnitude (max magnitude 4.1). The epicentral distribution of both isolated events and seismic sequences, disclose NE-SW striking active faults that fall in between the fault segments of the large historical earthquakes which occurred in the area. The available information on the stress field deducible from the focal mechanisms of the area agrees that a general extensional stress regime is acting. Locally both NE-SW and NNW-SSE extensions are observed. The large scale stress regime deduced from the focal mechanisms of strong instrumental earthquakes which occurred in the Apennines supports the local NE-SW extension but cannot explain the normal movements related to a NW-SE extension. The local longitudinal extension observed, supported by GPS data, can be explained utilizing large scale geodynamic models.