Estimating macroseismic intensity from documentary sources using Fuzzy Sets

Seismic intensity of historical earthquakes is usually assessed from documentary sources by the expert evaluation of the correspondence of reported effects with the descriptions of the adopted macroseismic scale. This process involves a number of subjective assumptions, not always explicitly stated, that sometimes may bring different experts to discrepant outcomes. We already proposed a decision making method, based on the fuzzy set theory and computer-aided procedures that can be successfully used to objectively assign macroseismic intensity. This approach is structured in three main steps: 1) the creation and computer coding of a dataset of effects for each locality, 2) the formulation of a set of rules to equate formally distinct macroseismic descriptions actually corresponding to the same effect 3) the application of a decisional algorithm to assign the intensity. The first two steps have now been improved and made friendlier, with respect to previous works, by the use of MS-Excel macros for data collection and management. We also applied and compared different decision algorithms and defuzzyfication methods using the data of some earthquakes of last century in Italy. Our analysis highlighted “strong” effects well correlated with a specific intensity degree for all the analyzed earthquakes and other “weak” effects which association with the intensity degrees depends on the considered earthquake.