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