Testing normal fault growth models by seismic stratigraphic architecture: The case of the Pliocene-Quaternary Fucino Basin (Central Apennines, Italy)

Normal faults grow either by radial propagation and segment linkage or by accruing displacement without a proportional increase in fault length. To test these competing models of fault growth, a novel 2D seismic stratigraphic interpretation of the recent Fucino Basin of the central Apennines (Italy) has been performed. The Fucino is a major Pliocene-Quaternary non-marine 'extensional col lapse basins', developed immediately after the Apenninic compressional strain had locally abated, and bounded by seismogenic faults that generate strong (Mw = 6-7) and destructive earthquakes. The Fucino is an overall dual polarity half-graben, built around two border fault systems: the northern one lies along the east-northeast striking Avezzano-Bussi regional fault-zone; the other, south-eastern trending, bounds the basin to the east. Two separate fault-driven depocentres of fluvio-lacustrine sequences (maximum thicknesses of similar to 1,750 m) are present. One is associated to the northern border faults, with mainly Late Pliocene activity; the second is to the hanging-wall of the eastern border-faults and reveals a stepwise Pleistocene-Recent activity. Tectonic depocentres have migrated clockwise through time, and new-born fault systems have developed at the south-eastern basin periphery (Gioia dei Marsi area). This, together with the progressive accumulation of throw in time without significant fault lengthening, suggests that the model of fault growth by segment linkage is not the best explanation for this basin. Instead, the stepwise onset and growth of the Fucino extensional collapse faulting, and its ongoing earthquake hazard, may have been promoted by polyphase inversion tectonics of inherited deep-seated zones of weaknesses (e.g. Avezzano-Bussi Line).