Page:Popular Science Monthly Volume 74.djvu/141

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earthquake of 1783 possessed likewise this double character, but in that instance also the areas of the heavy shocks were distinct though adjacent.

For purposes of study the latest Calabrian earthquake appears to offer some exceptional opportunities. The peculiar outlines of the two land masses which are involved render them specially open to study from the sea as a base. The full importance of this fact will be appreciated by any one who has been compelled to find accommodations where only the ruins of hotels exist. Under such circumstances one must proceed on foot or with a donkey, carrying supplies of bread and wine with him.

A scientific party engaged in studying the Calabrian earthquake could live for most of the time upon a vessel from which the shore would be reached either at the numerous ports or by launches. If a government vessel is to be sent with supplies to the afflicted district, the opportunity should not be lost to despatch a scientific party aboard her.

For another reason the recent earthquake offers unique opportunities for study. It has long been known that the straight eastern coast line of Sicily corresponds to a great zone of faulting within the earth's crust, and more than once in the past the slips upon it have brought disaster. On at least one such occasion, the sea bottom between Messina and Reggio and between Charybdis and Scilla has been considerably modified. In the vicinity large strips of cliff have slipped down into the deep sea at their base. A primary object of a scientific party charged with the investigation of this earthquake should, therefore, be to carry out an elaborate series of soundings in waters within and about the straits of Messina. Fortunately the dangerous nature of this channel is responsible for accurate data which represent the late condition. We have, therefore, here the opportunity of determining by a simple re-survey the changes which are ascribable to the recent earth disturbance.

A second section of the expedition should have for its chief object the preparation of maps of all portions of the shores or inland areas which reveal any change of configuration as a result of the earthquake. One of the most difficult of questions which arise in connection with earthquakes is to determine the exact significance of the so-called "secondary cracks." These cracks are generally found in loose materials, and the question is in how far they represent the projection upon the earth's surface of cracks within the consolidated rock below, or in how far they are due to settlement, and have in consequence less significance of orientation. This question can be definitely settled only by the aid of careful and detailed maps, which are studied in con-