Web-based macroseismic survey: fast information exchange and elaboration of seismic intensity effects in Italy

A new method of macroseismic survey, based on voluntary collaboration through the internet, has been running at Istituto Nazionale di Geofisica e Vulcanologia (INGV), Italy, since June 2007. The macroseismic questionnaire is addressed to a single nonspecialist person and reported effects are statistically analysed to extrapolate the Mercalli-Cancani-Sieberg (MCS) scale and the European Macroseismic Scale (EMS) intensity referred to by that observer. Maps of macroseismic intensity are displayed online in almost real time and are continuously updated. The aim of the questionnaire is to evaluate seismic effects as felt by the compiler. The final result is a definition of a particular degree of intensity with an evaluation of an associated uncertainty. Results of medium to low magnitude earthquakes are presented here, showing the ability of the method to give fast and interesting results. Effects reported in questionnaires coming from towns are analysed in-depth and assigned intensities are compared with those derived from traditional macroseismic surveys, showing the reliability of the web-based method