Page:Popular Science Monthly Volume 86.djvu/450

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HE recent Italian earthquake, which occurred on January 13 at a cost of 30,000 lives and $60,000,000 in property, calls attention to the fact that the most disastrous shocks of this sort are, in general, not connected at all with volcanoes or volcanic areas. This is contrary, of course, to the view widely held that all earthquakes are caused by, or in some way connected with, volcanic activity. In disproof of this view may be mentioned the great Calabrian earthquake of 1783. This great earthquake occurred in southwestern Italy, but in no wise affected the volcanic areas, and this is also true of the terrible Messina earthquake of 1908, which, though it devastated various towns and cities in that part of Sicily not far distant from Mount Etna, arose from earth movements in the Strait of Messina. It was not at all connected with Etna, which at that time exhibited no unusual volcanic activity, and, too, there were no other evidences that could possibly suggest its connection with the earthquake just alluded to.

The recent earthquake which first occurred east of Rome in the Abruzzi district was followed by severe shocks in the province of Calabria. Neither Vesuvius nor Etna is reported as exhibiting any special activity. Indeed it is evident that they are in no way connected with these shocks which have been so appallingly destructive of life and property.

Broadly speaking, there are two types of earthquakes, namely, the volcanic, which is due to shocks accompanying volcanic explosions, and the more disturbing and disastrous tectonic type, caused by faulting and Assuring accompanying warping of the earth's so-called crust. In Italy, these tectonic earthquakes, such as the Calabrian earthquake of 1783, the Messina earthquake of 1908, and the recent earthquake that wrought such destruction in the Abruzzi district are all of the tectonic type, and all are the result of earth fractures brought about by mountain-making movements. In this connection it will be of interest to consider just what areas of the earth are affected in this way, and why, in certain regions, earthquakes both occur and recur, while, on the other hand, similar earth movements are not experienced nor to be anticipated in regions where mountain-making movements are no longer actively in progress.