Earthquakes in medieval Sicily. A historical revision (7th-13th century)

Abstract

The need to understand the activity of the main seismogenetic structures, to calculate the recurrence periods of major earthquakes and to identify their main epicentral areas, requires wide-ranging research in the field of historical seismology. The present research was conducted in the framework of the projects of the Istituto Nazionale di Geofisica (1991-1995). The presence of different populations and ruling élites, and hence of languages and cultures, has in many cases confused the historical context of the medieval Sicilian sources. However, by going beyond the local sources, and analysing the events in a wider European and Mediterranean context, taking due account of the Byzantine, Latin and Arab sources, it has been possible to identify five seismic events that do not exist in the Italian catalogues or whose dates are very difficult to establish. Six spurious events have been deleted thanks to the revision (659, 785, 796, 963, 1069, 1259); the date of an event has been corrected (1140 into 1125) and five unknown events have been discovered: 853, 1172, 1203-1204, 1255-1256 and 1295-1296. The data on which these findings are based are in many cases dispersed and unused within the many specialised sectors of historical research; in some cases they are unknown even to historians. An example of textual analysis of the sources is also presented to show by what a roundabout route the chronological parameter for the 1125 earthquake was reached. The new events confirm the high seismicity of the eastern area of Sicily; nevertheless, the newly identified series does not seem to show any seismic event comparable to the one that struck the Messina Strait, in 1908 (I0 = XI MCS, M = 7.2): this historical element can provide information regarding the return times of such great event; a hypothesis is formulated by the authors: it will have to be carefully examinated by archaeology research. The criteria used in this research are explained, as well as the problems tackled in accordance with the method for the revision of the historical earthquakes adopted by ING-SGA.