Another step in the path from macroseismic fields to probabilistic modeling of attenuation

It is beyond doubt that information provided by historical seismology can provide a valuable aid to understanding the evolution of the seismic phenomenon; we cannot therefore renounce to analyze macroseismic intensity data in order to assign the seismic hazard of an area; well aware that this requires the development of specific models and techniques different from those adopted in the study of instrumental data. In this context the issue of macroseismic attenuation is also included. From the beginning of the 2000s, a path has been undertaken in the direction of probabilistic modeling of macroseismic attenuation, from the perspective of treating the whole process as random and not only of adding of a Gaussian error to the empirical relationships between magnitude, distance and intensity at site. In fact, the irregularities in the shape and extent of macroseismic fields depend on various factors and their potential interactions, like topography, pattern of population density, characteristics of regional geology, that cannot be reduced to a measurement error. Among the cornerstones of this approach there is the respect, as far as possible, of the ordinal nature of macroseismic intensity. According to this assumption, the intensity at any site is considered as an integer random variable that varies between one and the epicentral intensity.