Investigation of the active Celano-L'Aquila fault system, Abruzzi (central Apennines, Italy) with combined ground-penetrating radar and palaeoseismic trenching

We studied fault scarps along the northern sector of the Celano- L'Aquila fault system in the Abruzzi region (central Apennines). Up to similar to9.5 km long, 3 m high, fault scarp traces mark the slope foot of ridgetop valleys at Mt Ocre range. In order to provide direct evidence of the deformation history of these scarps, we initiated geomorphic, ground-penetrating radar (GPR) and trenching investigations. GPR investigations yielded subsurface stratigraphic features of the scarp zones, and determined the locations for trenching sites. A total of five trenches were excavated at two different sites. Structural and stratigraphic analysis of the trench exposures combined with historical considerations, showed three faulting events between 5620 BC and 1300 AD; the most recent of them occurred after 1690 BC. Each of these events produced an estimated minimum vertical displacement ranging between 0.3 and 0.5 m. Our interpretation is that the Mt Ocre fault branch represents the northernmost surface expression of a single 35 km long seismogenic structure associated with M similar to 7 earthquakes. Any attempt to estimate the seismic hazard in the area must consider the presence of this important source.