Faulting of the Roman aqueduct of Venafrum (southern Italy): Methods of investigation, results, and seismotectonic implications

We present evidence of surface faulting of a poorly known first-century B.C. aqueduct in central-southern Italy. Data were acquired by means of geological, geophysical, and geodetical surveys along the surficial trace of a primary active fault (Aquae Iuliae fault). The ~30-km-long Venafrum aqueduct presents a net vertical offset of almost 4 m at the intersection with this normal fault. This fact reveals the occurrence of repeated faulting of the Roman water supply after its construction, i.e., during large historical earthquakes, the last being one of the most violent events to happen in Italy during the Middle Ages (September 1349, Mw = 6.6). We tentatively associate the remaining offset of the aqueduct to other poorly characterized earthquakes in the area, which were not previously associated with any active fault. It is a well-known fact that the recognition of ancient earthquakes on archaeological relics is a matter of debate in archaeoseismology, being difficult at all times—and often impossible—to ascertain whether the damage observed should be related to seismic shaking or other causes (i.e., wars, floods, fires, decadence, etc.). Conversely, the exceptional case represented by the faulting of an archaeological relic such as this provides certain and reliable data on the causative seismogenic source and the associated earthquakes.