Surface faulting in the southern Italian Campania-Basilicata earthquake of 23 November 1980

Abstract

The Campania–Basilicata earthquake of 23 November 1980 was the largest (Ms =6.9) and most destructive earthquake that has occurred in this region of southern Italy for over 100 years, killing more than 3,000 people. The consensus among seismologists, geologists and earthquake engineers who have studied^1–10 this event is, in keeping with previous Italian earthquakes, that it did not produce faulting at the surface. This has led to the establishment of a number of models^2,3,11–13 requiring an unusual tectonic setting for the southern Apennines. However, on a recent visit to the epicentral region of the earthquake (May 1984), we discovered more than 10 km of surface faulting that is consistent with focal mechanisms for this event, based on first motion polarities^2,4,5,12 and long period waveform studies^14–16, which show that it involved normal faulting with one nodal plane dipping at ∼60° towards the north-east. Our observations of this—the first well-documented earthquake fault break to be reported in Italy—suggest that the deformation associated with earthquakes in the southern Apennines takes place in the upper 10–15 km of the Earth's crust on steep planar normal faults which break the surface, as is widely observed in other areas of active extension outside Italy.