Il periodo sismico della Sicilia occidentale iniziato il 14 Gennaio 1968

The memoir begins with a brief report on the activity<br />carried out by the Istituto Nazionale di Geofisica on the occasion of the<br />earthquakes, which violently hit numerous villages in West Sicily as from<br />January 14th 1968: the full development of the seismological crisis was unceasingly<br />followed by the seismological Observatory in Rome, which documented<br />the phenomenon with instrumental surveys and calculations. A<br />few days after the first shocks, the I.N.G. provided for the installation of three<br />seismological stations around the meizoseismal area (the station in Palermo<br />which had been damaged by the first violent shocks was rearranged and two<br />more were installed, one at Trapani and the other at Agrigento) for the purpose<br />of following the course of the long series of aftershocks even in their<br />slightest manifestations.<br />The memoir contains the results of observations carried out in respect<br />of the more severe shocks (survey of registration times, magnitude and epieentral<br />intensity) and gives a graph indicating the recurring frequency of<br />the earthquakes, day by day, up to June 10th 1968.<br />Figure 5 shows the position of some epicentres calculated by the Istituto<br />Nazionale di Geofisica (I.N.G.), the Bureau Central International de Seismologie<br />(B.C.I.S.) and by the United States Coast and Geodetic Survey<br />(U.S.C.G.S.). The epicentre map may be compared with the tectonic map<br />of the area.<br />The macroseismic feature of the phenomenon is duly emphasised.<br />After a concise survey of the most important effects caused by the shocks<br />of greatest intensity (a survey rendered most difficult by the frightening<br />rapid succession of events) the memoir sets forth the results obtained by<br />means of studies and calculations based on the damages officially ascertained<br />by the Genio Civile Offices.<br />As it was impossible to draw a chart of isoseismical lines, a chart of<br />lines of even damage (isoblabe) has been drawn (Pig. 6) and it summarizes<br />the global effects of the whole series of shocks with respect to buildings. It<br />is followed by an accurate and detailed analysis of results achieved.<br />Finally the seismic precedents of the localities affected are resumed,<br />with particular reference to the Belice Valley and Palermo area.

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