Surface rupture of the 1857 Southern Italian earthquake?

In October 1862, Robert Mallet published an extensive study of a large earthquake that occurred on 16 December 1857, 150 km south-east of Naples. This event is one of the most destructive ever recorded in Italy. Although continental earthquakes of similar size are almost invariably associated with surface faulting, Mallet did not identify any surface rupture and subsequent workers have also failed to find surface traces. Using satellite images and aerial photographs as a guide, we examined two prominent Quaternary normal fault systems in the field. Flanking the Val d'Agri and the Val di Diano, both trend NW-SE and dip to the SW. The distribution of damage suggests that one or both moved in 1857. On one fault segment in Val d'Agri, we found a 2.5-m high scarp whose youthfulness and height suggest it is due to the 1857 earthquake. Comparison of the observed slip with rates derived from geomorphic evidence suggests a recurrence time for 1857 type events of about 3000 years. While the new data we provide are consistent with the event having a magnitude of M(s) ~ 7.0, there are also grounds for supposing it might have been bigger.