Deriving numerical estimates from descriptive information: the computation of earthquake parameters

We describe here how the origin time, the epicenter location, the epicentral intensity and the magnitude of the earthquakes included in the Catalogue of Strong Italian Earthquakes (CFTI3) have been determined from the documentary information available. As the literature lacks widely accepted formal definitions for these parameters in the case of macroseismic data, we developed ad hoc procedures that starting from generally shared qualitative statements give reasonable and stable results which can also be useful for statistical analysis. These procedures use all of the information available in the CFTI3 database as much as possible and make use of "robust" estimators in order to minimize the effects of anomalous data. The resulting parametric catalogue has been examined statistically for completeness showing that the great majority of the Italian earthquakes with moment magnitude larger that 5.5-6.0 of the last four centuries are correctly reported in CFTI3