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

This paper examines the 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 of two segments: a N-NNW-trending longer segment and a N100°-trending segment. After developing as a normal fault in the Early Pleistocene, the N-NNW Martana Fault segment experienced a phase of dextral faulting extending from the Early-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 s3 axis and NW-NNW s1 axis in the Late Pleistocene-Holocene 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 evidence ongoing activity of this fault. The active left-lateral kinematics along N-NNW-trending fault segments are also revealed by the 1.8 m horizontal offset of the E-W-trending Decumanus road, at the Roman town of Carsulae. We interpret the present-day kinematics of the Martana Fault as consistent with a model connecting surface structures to the inferred NNW-trending lithospheric shear zone marking the western boundary of the Adria Plate.