Children of a Lesser Seismological God: The 1971 Tuscania (Central Italy) "Historical" Earthquake

The 6 February 1971 Tuscania (central Italy) earthquake belongs to a peculiar family of destructive seismic events that have occurred in an area classified as low-seismic hazard, causing heavy damage and tens of casualties. However, this earthquake took place at the dawn of modern seismology in Italy and is far from being fully characterized from an instrumental and macroseismological point of view. This article aims at bridging the gap of information that affects that earthquake, through a twofold research path: (1) with an archival investigation looking for new available sources and with the use of the European Macroseismic Scale-98 (EMS-98) intensity scale, and (2) with the calculation of a more constrained hypocentral location. The results of this investigation can be summarized as follows: the reappraisal of the earthquake in terms of EMS-98 provides a maximum intensity 8 in Tuscania (previously quoted 8-9 Mercalli-Cancani-Sieberg [MCS] in the catalog), and a general decrease of intensity in many damaged localities. The new epicenter location is shifted almost 10 km southeast of the old one, at about 3 km depth. This new location is more robust than the previous one and is consistent with the general distribution of the most damaged localities; however, we cannot exclude that effects of directivity might have played a role in the peculiar pattern of damage caused by the event. Finally, we provide new values of magnitude (M-D 4.9 and M-L 5.1) that point to an upward scaling of the earthquake. The ultimate lesson of this work is that a deepening of the research can always provide room for an improvement of our knowledge even for significant earthquakes that have occurred relatively recently.