Page:Popular Science Monthly Volume 68.djvu/570

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It is too late to describe here the appalling disaster that has overtaken San Francisco and the neighboring regions and too soon to attempt to present a scientific survey of the causes leading to the catastrophe and the precautions that should be taken to avoid its recurrence. We can but add one more expression of the universal sympathy and a further appreciation of the undaunted courage which leads men to assert their supremacy even in the face of the most terrible exhibition of the powers of nature.

The progress of science and the conditions of modern civilization have been the chief causes of the calamity; yet we may confidently look to the same factors to prevent its recurrence. Earthquakes occur daily, and a shock such as that of April 18 would have done but small damage to a farming community. The trouble was due, on the one hand, to large piles of masonry or flimsy brickwork unsuited to resist vibrations, and, on the other, to the conflagation. The live electric wires, the methods of heating, lighting and applying power, the dependence of a modern city on its fire department and a supply of water through mains, not only explain the San Francisco fire, but made it almost inevitable. On the other hand, the steel frames and concrete reenforced with steel wires, proved themselves, as had been foreseen, well fitted to resist destruction. The only trouble was the shaking off of the stones and bricks and the inflammable contents. If it were not for the esthetic effects, such buildings might be covered with metal sheathing and be made fire-proof within as well as without. They would then be earthquakeproof—at least for such shocks as are known to have occurred—and would be as effective as open spaces in stopping the spread of a conflagation. San Francisco will take all needful precautions. Whether cities less likely to suffer should do so is more doubtful. The effects of an earthquake in New York City would be appalling. The people would rush into the streets, too narrow to hold them, while the stones would be shaken down on their heads, the conditions being similar to those of a vast theater fire. But more lives are needlessly sacrificed in New York City each month than have been lost in the California disaster, and more money is wasted each year than is needed to rebuild San Francisco.

The causes of earthquakes are somewhat obscure and are doubtless of different kinds. They are part of the vast terrestrial phenomena which have lifted the continents and the mountain ranges. The main stresses may be due to contraction of the crust of the earth or to changes in its shape, while the proximate causes are the local geological formations. The conditions at San Francisco are fairly well understood. There is a fault in the peninsula along the Portolá Valley, where for about forty miles the rocks on one side have at some time sunk two thousand feet. At the time of the recent earthquake, the land on the west side of the fault was forced northward from three to six feet, and the violent dislocation accounts for the shock. Mr. G. K. Gilbert has been instructed by the U. S. Geological Survey to make a thorough study of the causes, and we