Earthquakes and fault(s) in the Upper Ofanto Valley (Irpinia, southern Italy)

Thirty years ago - on November 23, 1980 - the strongest earthquake (Mw 6.9) occurred in the 20th century in the southern Apennine rocked the villages of the Upper Ofanto Valley (Irpinia), causing almost 3000 fatalities. Indeed, this small region is one of the most seismically active of Europe; for instance, Conza della Campania - one of its more ancient settlement - has been struck at least seven times (Is>VIII MCS; GALLI, 2010) during the past millennium, each time rising again over its ruins. But after the 1980 earthquake, it has been deserted, and rebuilt by its inhabitants 1 km away from its former, pre-Roman settlement. Many of these earthquakes are almost unknown, and some do not still appear in the current seismic catalogue (CPTI, 2004); others are well characterised in terms of intensity distribution, but still lack any certain seismogenetic attribution. Only the 1980 one has conclusive data concerning its causative seismogenic structure, not only due to the large amount of instrumental data, but also because of the unequivocal surface faulting phenomena that drew the attention of some geologists on a previously unconsidered fault system (i.e., Mt. Marzano fault, and contiguous segments: MMFS. WESTAWAY& JACKSON, 1984). On the basis of 1) field study on faults and fault scarps and 2) archive research of minor earthquakes, we are currently trying to cast light on these aspects, which are both the basic ingredients for understanding the seismic hazard of the region.