Deformation of a Roman Aqueduct (II-III Century A.D.) near Rome, Italy

Along the modern trace of the Tiburtina road, approximately 20 km north-east of the city of Rome, recent archaeological diggings have brought to light a system of aqueduct galleries constructed by roman engineers (II-III century A.D). Two narrow water channels (A and B) of this aqueduct system were strongly deformed by tectonic movement that occurred subsequent to their construction. The archaeological site falls inside the Acque Albule basin (AAB): a travertine plateau, upper Pleistocene in age with a medium thickness of approximately 60 m. The AAB has been interpreted as a rhomb-shaped pull-apart basin (7 km long, 4 km wide) created by strike-slip faulting within a N-S shear zone that crosses the Rome area. Its evolution is attributed to Middle-Upper Pleistocene times. The principal N-S water channel (A) evidences both brittle (extensive) and ductile (compressive) deformations, whereas the shorter channel (B) to the south-west reveals predominantly ductile deformations associated with compression. A detailed survey of the A channel indicates a segmented course along the length of the entire structure, with orientations ranging between N10°E and N10°W, and with one section oriented at N35°W. The smaller B channel situated to the south-west of the principal excavation indicates that deformation can be linked to transverse compression resulting in a restriction and rotation of the structure. The geometry of the deformation pattern and the brittle structures affecting the surrounding rock, the presence of sections deformed in a ductile manner, the segmentation of the two channels into tracts rotated in different directions, the narrowing of an internal section of the B channel orientated N15°W, are all elements compatible with strike-slip tectonics. To provide additional quantitative support for these observations, 3 sites (35 samples) were drilled, for paleomagnetic and anisotropy of magnetic susceptibility analyses, in the "Pozzolane Rosse" Formation (457+/-4 kyr). With respect to a few years ago, when the Roman volcanoes were considered extinct and with no signs of active tectonic activity present in the area, it seems today that the Eternal City is not still destined - geologically speaking - to eternal rest!