Macroseismic intensity evaluation for the seismic hazard assessment in the third millennium.

Abstract

The aim of this paper is to highlight the importance of the proper assessment of macroseismic intensity evaluation of earthquakes, that can be considered “ethical” for defining the seismic hazard of a region. The macroseismic intensity represents the classification of the earthquake effects on people, buildings, and also on the natural environment. The intensity evaluation of an earthquake is, even today, essential for two reasons: the first one is related to the time window, since the intensity values include a period of time of thousands years (from the paleoseismological and historical earthquakes, to the recent ones) while the magnitude estimates are available only since the middle XX century; the second reason is that the intensity allows us to assess the macroseismic effects also where buildings are absent (for example in desert areas) considering only the environmental effects. Currently, nearly a hundred of macroseismic scales are available and used worldwide (Gaudiosi et al., 2014). Italy, characterized by high seismicity level, shows old traditions in the classification of effects induced by the seismic events. Actually, some of the oldest cartographic representations, such as a map of the 1564 earthquake in the Nizza area (France), and the maps of the great Apulian 1627 earthquake (De Poardi, 1627; Greuter 1627) could be considered as authentic forerunners of the modern macroseismic scales. The first intensity scales accepted across the world were the de Rossi-Forel (1883) and the Mercalli scales (1902). The common macroseismic scales such as the de Rossi-Forel, the Mercalli, the MCS, the Modified Mercalli and the MSK scales estimate the effects on the environment as diagnostic elements relevant for evaluating the intensity degree of the earthquakes. These scales are nowadays supported by the new Scale ESI 2007 (Michetti et al., 2007) that assign the intensity only on the basis of the effects triggered by earthquakes on the natural environment. Actually, recent studies have provided clear evidence that geological and environmental effects, which have been currently collected in up-to-date database, provide essential information for intensity assessment and therefore they represent a valuable contribution to the seismic hazard definition.