Some remarks on the Umbria-Marche Earthquakes of 1997

Aim of this paper is the investigation on the main characteristics and the consequences of the seismic sequence which caused considerable damage in the central part of Italy on September and October 1997. The time evolution, in terms of released energy, magnitude and macroseismic distribution was first analysed. Then, a study of the seismic history of Umbria-Marche Apennine was performed, in order to gain a better comprehension of such distinctive seismic sequence, and to highlight some seismologic characteristics of the region. As the evaluation of the destructive potential of the ground motion requires the knowledge of a significant index of the distance from the source, it was necessary to formulate a preliminary hypothesis of the geometry of the source and of its spatial position. Starting from the trace of the assumed source, considering an extensive mechanism and accepting the hypothesis of evolution of the process of rupture, the strong ground motion derived from the accelerometric records, including a significant example of site effects, was investigated. Finally, in the areas the most hardly hit by the earthquake the damage in masonry buildings was analysed.