Reducing the subjectivity of intensity estimates: The fuzzy set approach

We describe a method for the encoding and the computer analysis of the macroseismic effects deduced from historical sources allowing the complete formalization of the process of seismic intensity assessment. It makes use of a multi-criteria decisions-support algorithm, based on the theory of the Fuzzy Sets. Analyzing the texts of the available sources for the 1919 Mugello (Ms = 6.2) and 1920 Garfagnana (Ms = 6.5) earthquakes, the observed effects are classified independently of any macroseismic scale. Each sentence reported on the sources is ≪decomposed≫ into five syntactic elementary components and represented by a set of alphanumeric codes for further processing by computer codes. This retains the maximum adherence to the original sources and avoids forced interpretations and losses of information due to the need to fit each observed effect to a description of the scale. Moreover, this scheme also allows to gather equivalent effects by reassigning them the same code, and using this new classification in further processing. This procedure could even be useful to define a new macroseismic scale on the basis of a statistical analysis of different effect occurrences.