earthquakes: a growing contribution to the Catalogue of Strong Italian Earthquakes

The particular structure of the research into historical seismology found in this catalogue has allowed a lot of information about unknown seismic events to be traced. This new contribution to seismologic knowledge mainly consists in: i) the retrieval and organisation within a coherent framework of documentary evidence of earthquakes that took place between the Middle Ages and the sixteenth century; ii) the improved knowledge of seismic events, even destructive events, which in the past had been "obscured" by large earthquakes; iii) the identification of earthquakes in "silent" seismic areas. The complex elements to be taken into account when dealing with unknown seismic events have been outlined; much "new" information often falls into one of the following categories: simple chronological errors relative to other well-known events; descriptions of other natural phenomena, though defined in texts as "earthquakes" (landslides, hurricanes, tornadoes, etc.); unknown tremors belonging to known seismic periods; tremors that may be connected with events which have been catalogued under incorrect dates and with very approximate estimates of location and intensity. This proves that this was not a real seismic "silence" but a research vacuum