Fig. 42. Map of the Calabrian Earthquake of 1783
As can be seen by an examination of the map presented in [Fig. 42], the part of Italy included in the Calabrias covers an area from north to south almost equal to two degrees of latitude. Although the shock extended beyond the limits of Calabria, since it reached as far north as Naples, as well as over a great part of the Island of Sicily, the territory in which the greatest damage was done did not exceed in area about 500 square miles.
The southern part of Italy is subject to frequent earthquake shocks. Pignatari, an Italian physician, asserts that this region was visited during 1783 by no less than 949 earthquakes, of which 501 were of the first class, or degree of intensity, while in 1784, there were 151 earthquakes, of which ninety-eight were of the first class.
It seems that the city of Oppido, marked on the above map as midway between the two coasts, was the point from which the severe earthquake of 1783 started. If one draws a circle, with a radius of twenty-two miles, around Oppido as a centre, the portions of the Calabrias that were the most affected will all lie within this circle.
The great Calabrian earthquake was attended by numerous shocks. The first and the most severe shock, that of February 5th, 1783, was only two minutes in destroying most of the houses in all cities, towns, and villages on the western side of the Apennines in this part of Italy.
Another severe shock occurred on the 28th of March. This shock was almost as severe as that of February 5th.
In order to understand many of the effects produced by this earthquake, inquiry must be made into the geological character of the region. According to Dolomieu, the flat country at the slopes of the Apennines, known as the Plain of Calabria, is covered with sand and clay mixed with sea shells. These strata have been deposited by the sea from materials that have been obtained by the decomposition of the granite mountain ranges in the Apennines. The plain is quite level except where it is crossed by deep valleys or ravines, which have been eroded or cut by the swift mountain torrents. In many cases, these ravines or valleys have depths as great as 600 feet. Their sides are generally almost perpendicular. Consequently, as Lyell remarks, throughout the length of the mountain chain, the soil, which adheres but loosely to the granite base of the mountain chain, could therefore be easily separated from the mountain, and sliding over the solid steeps of the mountain could readily move, especially through the ravines or gorges, to distances in some cases as great as from nine to ten miles.
This peculiarity of the country must be thoroughly understood, since, otherwise, it would seem impossible that lands could be carried several miles from their former position, and often bear along with them almost undisturbed houses, olive groves, vineyards, and cultivated fields.
The heaving of the surface of the earth like the waters of the sea, so common in severe earthquakes, occurred during the Calabrian earthquake. In some places this heaving so shook the trees that they bent until their tops touched the ground near their base.
Parts of the ground were violently thrown upwards into the air as in the explosive type of earthquakes. In many instances the large paving stones were thrown into the air and afterwards found with their lower portions upwards.