Seismic scenarios and assessment of intensity: some criteria for the use of the MCS scale

Abstract

The macroseismic scale used for the classification of the more than 33100 seismic effects of the Catalogue of Strong Italian Earthquakes (CFTI3) is the Mercalli Cancani Sieberg (MCS). As in all scales, the use of the MCS scale in determining the macroseismic intensity of historical earthquakes involves difficulties regarding the classification of descriptions of a quality nature. These descriptions often lack standardisation as regards levels of information and the semantic value of the statements, and there are also various levels of description of the damage in relation to the various economic and building contexts. As is known, the intensity scales were compiled to classify the effects of earthquakes contemporary to the observers. The scales are therefore classification tools designed to be applied from direct observations. The general criteria used in assessment of the intensity degrees are those of a direct comparison between the descriptive outlines gained from historical research and the descriptions given by the different degrees of the scale. While this is true in a general sense, there are a number of cases where the interpretation may vacillate when the context examined contains no elements of clarification, in relation to the levels of detail of the research or the context. To understand how the many problems connected to the assessment of intensity of seismic scenarios carried out from historical sources have been solved the criteria applied are here described.