Geological and archaeological evidence of active faulting on the Martana Fault(Umbria-Marche Apennines, Italy) and its geodynamic implications.

This paper examines th0e morphotectonic and structural-geological characteristics of the Quaternary Martana Fault in the Umbria-Marche Apennines fold-and-thrust belt. This structure is more than 30 km long and comprises two segments: a N-NNW-trending longer segment and a 100°N-trending segment. After developing as a normal fault in Early Pleistocene times, the N-NNW Martana Fault segment experienced a phase of dextral faulting extending from the Early to Middle Pleistocene boundary until around 0.39 Ma, the absolute age of volcanics erupted in correspondence to releasing bends. The establishment of a stress field with a NE-ENE-trending σ3 axis and NW-NNW σ1 axis in Late Pleistocene to Holocene times resulted in a strong component of sinistral faulting along N-NNW-trending fault segments and almost pure normal faulting on newly formed NW-SE faults. Fresh fault scarps, the interaction of faulting with drainage systems and displacement of alluvial fan apexes provide evidence of the ongoing activity of this fault. The active left-lateral kinematic along N-NNW-trending fault segments is also revealed by the 1.8 in horizontal offset of the E W trending Decumanus road, at the Roman town of Carsulae. We interpret the present-day kinematics of the Marlana Fault as consistent with a model connecting surface structures to the inferred north-northwest trending lithospheric shear zone marking the western boundary of the Adria Plate.