Active tectonics in the central Apennines and possible implications for seismic hazard analysis in peninsular Italy

In peninsular Italy the central Apennines fault system (CAFS), overprinting earlier structures of a Neogene fold and thrust belt, includes segments characterized by diffuse seismicity distributed within a NNW-SSE trending, 50-60 km wide zone. The system has been analysed by means of morphotectonic and structural analysis of exposed active fault segments. The resulting fault structure consists of an interconnecting network of roughly N-S trending left-lateral strike-slip segments and mostly NW-SE oriented transtensional to normal faults. Evidence for recent activity of CAFS structures is provided by faulted Middle Pleistocene-Holocene deposits (including 30-40 ka old pyroclastites and 40 ka old palustrine sediments), fresh scarps in both bedrock and late Quaternary continental deposits, and decametric lateral offsets locally affecting the Post-Wurmian drainage pattern of the area. The regional stress field responsible for the development and evolution of the CAFS, as inferred from fault slip data, is characterized by a NW-SE compression and by a NE-SW extension. The CAFS pattern and its present day kinematics have been related to left-lateral strike-slip motion on north-south trending crustal faults. The existence of deep-seated strike-slip faults in the central Apennines has implications for seismic hazard analysis. Motion along these structures suggests, in fact, that coseismic surface faulting is distributed, and that cumulative displacements include normal, transtensional, and strike-slip components. The seismogenic potential of CAFS structures can therefore be best described by multiple-ruptures models and better analysed in terms of partial contributions of lower-rank features constituting congruent structural associations within the system.