Marazzi, Federico

Integration of archaeoseismic observations, geological and geophysical surveys and a critical review of historical written sources contributed to shed light on the effects of the 847 earthquake AD that struck a large area of Southern-Central Italy. New archaeoseismic evidence of a strong earthquake comes from two Medieval archaeological sites along the Volturno Valley, between Campania and Molise regions, which occurred around the middle of the ninth century AD. Evidence includes the tilting of pillars in the Basilica of Santa Maria near Alvignano (northern Campania) and a collapsed masonry wall in the Abbey of San Vincenzo al Volturno near Isernia (northern Molise). At Alvignano, a site so far unrecorded in seismic catalogues for the 847 earthquake, geoelectrical and georadar investigations were used to explore the subsoil and study local site conditions, which could have influenced coseismic ground motion. Integrated interpretation of geophysical surveys and borehole logs document the presence of altered pyroclastic deposits, which certainly enhanced site effects at Alvignano. Analysis of damage descriptions and of archaeological reports indicate that the 847 seismic event documented by historical sources damaged a wide area between Latium, Campania and Molise, with destruction of the town of Isernia. Although historical sources did not explicitly mention damage in Rome, seismic effects attributed to the 847 event are recorded in the archaeological and seismological literature. Because the damaged area for this medieval earthquake is loosely defined due to the scanty documentation, the present study represents an important contribution to better define the shaking area and provide new hints on the extent and location of the possible seismogenic source.