Earthquake

a sudden movement of the earth's surface. The passage of a heavy railway train creates a vibration, differing from an earthquake chiefly in intensity. The causes of earthquakes are various. Sometimes an extensive crack forms in certain rock strata, and the rock on one side of the crack settles; or else the roof of an extensive subterranean cavity falls in. Other shocks originate in disturbances arising from an outburst of volcanic lava. It is thought that nearly all earthquake movements originate within the upper ten miles of the earth's crust, and most of them within two or three miles of the surface. The destructive influence of an earthquake shock is due rather to its extreme quickness than to the extent of vibration. It is believed that no earthquake vibration ever reaches a foot in amplitude, and that the earth's crust moves usually but a very small fraction of an inch. The nature of an earthquake shock may be illustrated by giving a table a sharp, quick, light tap with a hammer. A marble lying on the table will bound to a height of several inches, although the surface of the table cannot have vibrated, itself, more than one-ten-thousandth part of that distance. In this way a slight tremor or jar of the earth is quite sufficient to fling people out of bed, throw dishes out of a pantry, or bring stone walls tumbling down.

No part of the earth's surface seems to be entirely free from earthquakes, although they appear to have been more frequent or else better observed near the seacoast. The list of recorded earthquakes now includes about 7,000. In the year 1876, for instance, there were 104.

In 1755 the city of Lisbon was almost blotted out of existence by a sea wave caused by an earthquake. In 1811 an earthquake visited the Mississippi Valley. Five thousand square miles in the vicinity of New Madrid were lowered ten feet on an average. Productive farms were converted into hopeless swamps and the owners were forced to seek homes elsewhere. One of the most notable earthquakes in the United States occurred at Charleston, South Carolina, August 31, 1866. Nearly one hundred people were killed. Several million dollars' worth of property was destroyed. In 1868 the coast of Peru and Ecuador was swamped by huge waves created by an earthquake shock. They poured over the land with a depth of sixty feet. The city of San Francisco was damaged by the same series of shocks. In 1891 Japan experienced a notable earthquake. A crack was traced for a distance of forty miles. The earth and rock sank from two to twenty feet along one side of the crack. In 1897 an earthquake visited India. Myriads of fish were killed in the Ganges as though by an explosion of a dynamite cartridge.

April 18, 1906, the region about San Francisco, California, was visited by the most destructive earthquake ever known in North America. The damage to public buildings in various towns of the vicinity was great. The destruction in San Francisco was simply appalling. Huge structures were shaken to the ground; water mains burst. To add to the horror fire broke out. Between earthquake and flames, eight square miles of buildings were almost entirely destroyed. The public buildings of the city, banks, hotels, an immense ferry station, and Chinatown were wrecked utterly. Two hundred thousand people were driven out of their homes. It is estimated that the loss of life reached 452 and that $200,000,000 worth of property was destroyed. Later in the same year a violent shock was felt on the coast of Chile, at Valparaiso and elsewhere.

In 1908 a terrible earthquake visited southern Italy. A region about seventy five miles in diameter, including the northeastern part of Sicily and the toe of Italy, literally shuddered and fell a few feet in to the bed of the ocean. The shock was so terrific that almost all buildings within this territory were shaken to the ground. Messina and Reggio, cities rising from the water's edge, tumbled in ruins. Huge tidal waves came up, covering the debris with mud and washing thousands of fugitives out to sea. Where mud did not flow in, fires broke out. In a few hours' time the homes of 200,000 people in these two cities alone were either buried out of sight, or converted into ashes. The greater number of the inhabitants never escaped from the ruins. In many of the small towns half of the people met their death. The catastrophe was so extensive and the loss of life so great that no accurate report will ever be possible, but it is estimated that 200,000 people lost their lives.

The following is a partial list of the notable earthquakes:

NOTABLE EARTHQUAKES.

Total . . . . . 1,392,552