Macroseismic intensity is a classification of the severity of ground shaking, based on observed effects within a limited area. Information on observations during an earthquake can be broken down into five categories – information on human beings, on objects, on buildings, on animals and on the natural environment – and these categories are numerically scaled. Several different systems are used worldwide: at present, the SED and many other similar organisations in Europe use the European macroseismic scale or EMS-98, so-called because it was introduced in 1998 (see Grünthal G., ed. 1998). An intensity scale provides a general indication of the impact of an earthquake, from the very weakest (with an intensity of I on the EMS-98 scale: 'Not felt') to the very strongest (with an EMS-98 intensity of X or more and classed as extreme). Each locality is assigned a single intensity. The resulting intensity map gives a comprehensive overview of the earthquake-impact pattern.
In principle, the subjective criteria used by the respective analyst also be factored in when assigning a site its intensity value. Consequently, it is important to document the evaluation procedure, declare any scope for interpretation and state any uncertainties. Accordingly, in practice the SED assigns each locality a range between a minimum (Imin) and maximum (Imax) value as well as a value with the highest probability (Iw), which serves as the basis for catalogue entries and maps.
Grünthal, G., ed. 1998. European Macroseismic Scale 1998 (EMS–98), Cahier bleu published by the European Centre for Geodynamics and Seismology (ECGS), vol. 15, Helfent-Betrange (Luxembourg)