THE COLFIORITO EARTHQUAKE SEQUENCE OF SEPTEMBER–OCTOBER 1997: SURFACE BREAKS AND SEISMOTECTONIC IMPLICATIONS FOR THE CENTRAL APENNINES (ITALY)

Between September–October 1997, a seismic sequence with three main shocks (Mw=5.6, 5.9, on September 26, and Ms=5.5 on October 14) struck the Umbria-Marche region in central Italy between the villages of Nocera-Umbra and Sellano. Although earthquake-induced landslides were observed and mapped in the epicentral area along the main active normal faults, no surface faulting was associated with the two first shocks of September 26. In contrast, the third shock of October 14 produced discontinuous coseismic tectonic ruptures (60 m–500 m long) along a total length of 5 km. Surface ruptures strike in the NNW-SSE direction, dip to the SW and show locally en-echelon geometry (either right-or left-stepping). Coseismic ruptures and active faults are in good agreement with CMT focal-mechanism solutions that indicate normal faulting for the three main shocks. These results provide additional information on surface tectonic ruptures caused by moderate-sized earthquakes, yielding some constraints on seismotectonic processes.     

ARCHAEOSEISMOLOGY IN ITALY: CASE STUDIES AND IMPLICATIONS ON LONG-TERM SEISMICITY

Four Italian cases from central Apennines and central-eastern Alps show how the use of archaeoseismology and paleoseismological investigations on deformed archaeological remains may improve the knowledge on long-term seismicity. In the Fucino Plain (central Apennines), the displacement of a Roman canal (built during the lst-2nd century AD) was caused by the movement of one of the active faults affecting the basin. The paleoseismological analysis and available archaeological data permitted to date the event at the 5th-6th century AD and to hypothesise that this earthquake was also responsible for significant damage to the Colosseum in Rome shortly before 508 AD. At the Egna site (Bolzano province, northern Italy), the displacement of a Roman building has been paleoseismologically investigated. It probably resulted from surface faulting, thus permitting to hypothesise the occurrence of strong earthquakes in an area for which seismicity does not show significant historical earthquakes. In the Sulmona Plain (central Apennines) the occurrence of a strong event around the middle of the 2nd century AD is testified by ah epigraph. Widespread evidence of building, collapses and abandonments characterise a number of archaeologically investigated sites and confirm the age of occurrence inferred from the epigraph. In the Trento area (northern Italy), evidence of earthquake-induced damage to medieval buildings suggests that the earthquake which affected northern Italy in 1117 may have been responsible for significant damage also in the Adige Valley. Gained experience indicates that in areas where historical research does not contribute significantly to the knowledge of the effects of strong earthquakes, the use of archaeological evidence of past earthquakes may be a valuable tool to obtain information on the historical seismicity related to moderate-large magnitude events.