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Probably no part of the earth’s surface is entirely free from vibration, but, fortunately, destructive earthquakes are confined to comparatively limited regions. In most cases each shock lasts only a few seconds, but the tremblings that follow may be continued for days, weeks, or even months. Noises of sundry kinds usually precede, accompany, or succeed an earthquake. Some earthquakes, however, are not attended by any subterranean sounds. This has been the case with some of the most destructive South American disturbances. Thus at the time of the terrible shock which destroyed Riobamba in Ecuador in 1797, a complete silence reigned. On the other hand, subterranean sounds may be heard without any earth-tremor being perceived.

The sound which accompanies many earthquakes is due to the transmission to the air of vibrations in the soil. To produce sound-waves in the air, the ground must vibrate like a drumhead. Hence no sound will be heard when the oscillations are horizontal.

The velocity of propagation of an earthquake is very variable. Thus in the case of the earthquake of Lisbon in 1755, it seems to have considerably exceeded one thousand feet per second, while in the Lisbon earthquake of 1761 the rate was three times greater. At Tokio, in 1881, the velocity, as estimated by Professor Milne, varied between four thousand feet and nine thousand feet per second.

Depth of Earthquakes. Various attempts have been made to estimate the depth at which earthquakes originate. Mallet was of opinion that the centrum of the Neapolitan earthquake of 1857 was probably five and one-half miles from the surface. The same eminent physicist thought that an earthquake centrum probably never exceeded a depth of thirty geographical miles. According to Professor Milne, the angles of emergence of the earth-waves obtained during the Yokohama earthquake of 1880 showed that the depth of origin of that earthquake might be between one and one-half and five miles; and he gives a table, compiled from the writings of various observers, which exhibits the mean depths at which certain earthquakes have originated. These estimated depths range from 17,260 feet to 127,309 feet.

The area disturbed by an earthquake is generally proportionate to the intensity of the shock. The great earthquake of Lisbon disturbed an area four times as great as the whole of Europe. In the form of tremors and pulsations, Mr. Milne remarks, it may have shaken the whole globe.

In a violent submarine earthquake the ordinary earth-wave and sound-wave are accompanied by sea-waves. These waves may be twenty, sixty or even eighty feet higher than the highest tide, and are usually more dreaded than the earthquake shock itself in such regions as the maritime districts of South America. The greatest sea-wave on record is that which in 1737, is said to have broken near Cape Lopatka, at the south end of Kamchatka, two hundred and ten feet in height.

NOTABLY DESTRUCTIVE EARTHQUAKES

79. One accompanied by the eruption of Vesuvius; the cities of Pompeii and Herculaneum buried.

742. Awful one in Syria, Palestine, and Asia; more than 500 towns were destroyed and the loss of life surpassed all calculations.

936. Constantinople overturned; all Greece shaken.

1137. Catania, in Sicily, overturned, and 15,000 persons buried in the ruins.

1186. At Calabria; one of its cities and all its inhabitants overwhelmed in the Adriatic Sea.

1456. At Naples, 40,000 persons perished.

1537. At Lisbon; 1,500 houses and 30,000 persons buried in the ruins; several neighboring towns ingulfed with their inhabitants.

1596. In Japan; several cities made ruins, and thousands perished.

1662. One in China, when 300,000 persons were buried in Pekin alone.

1693. One in Sicily, which overturned fifty-four cities and towns, and 300 villages. Of Catania and its 18,000 inhabitants not a trace remained; more than 100,000 lives were lost.

1726. Palermo nearly destroyed; 6,000 lives lost.

1731. Again in China; and 100,000 people swallowed up at Pekin.

1746. Lima and Callao demolished; 18,000 persons buried in the ruins.

1754. At Grand Cairo; half of the houses and 40,000 persons swallowed up.

1755. Quito destroyed.

1755. Great earthquake at Lisbon. In about eight minutes most of the houses and upward of 50,000 inhabitants were swallowed up, and whole streets buried. The cities of Coimbra, Oporto, and Braga suffered dreadfully, and St. Ubes was wholly overturned. In Spain, a large part of Malaga became ruins. One-half of Fez, in Morocco, was destroyed, and more than 12,000 Arabs perished there. About half of the Island of Madeira became waste; and 2,000 houses in the Island of Mytilene, in the Archipelago, were overthrown. This awful earthquake extended 5,000 miles; even to Scotland.

1759. In Syria, extended over 10,000 square miles; Baalbec destroyed.

1783. Messina and other towns in Italy and Sicily overthrown; 40,000 persons perished.

1797. The whole country between Santa Fe and Panama destroyed, including Cusco and Quito, 40,000 people buried.

1840. Awful and destructive earthquake at Mount Ararat, in one of the districts of Armenia; 3,137 houses were overthrown, and several hundred persons perished.

1842. At Cape Haytien, St. Domingo, which destroyed nearly two-thirds of the town; between 4,000 and 5,000 lives were lost.

1851. In South Italy; Melfi almost laid in ruins; 14,000 lives lost.

1852. At Philippine Isles; Manila nearly destroyed.

1853. Thebes, in Greece, nearly destroyed.

1854. St. Salvador, South America, destroyed.

1854. Amasca, in Japan, and Simoda, in Nippon, destroyed; Jeddo much injured.

1855. Broussa, in Turkey, nearly destroyed.

1857. In Calabria, Montemurro and many other towns destroyed, and about 22,000 lives lost in a few seconds.

1858. Corinth nearly destroyed.

1859. At Quito; about 5,000 persons killed, and an immense amount of property destroyed.

1868. Cities of Arequipa, Iquique, Tacna, and Chincha, and many small towns in Peru and Ecuador destroyed; about 25,000 perished.

1883. Krakatoa island, between Sumatra and Java, East Indies, was the scene of a series of volcanic discharges in May to August, 1883, constituting the most tremendous eruption known to history. A cubic mile of rock material was hurled into the air, and the explosions were heard 150 miles away. Violent atmospheric disturbances and gigantic sea-waves, the latter causing great loss of life, estimated at more than 30,000. As a result of the explosion, the north part of the island, including its highest peak, altogether disappeared.

1886. Shocks throughout eastern United States; at Charleston, S. C, 41 lives and $5,000,000 worth of property lost.

1893. Islands of Zante and Stromboli, the former west of Greece, the latter one of the Lipari group, west of Calabria, Italy, severely shaken. Great loss of lives and property at Zante.

1906. Severe shocks in California wrecked San Francisco and adjacent towns, and caused the greatest fire in history, lasting two days. Great loss of life, and $300,000,000 of property destroyed; over 300,000 homeless. Stanford University buildings were damaged to the extent of $2,800,000, including the fine Memorial Church.

1906. At Valparaiso, Chile, causing great destruction of life and property.

1907. Large part of Kingston, Jamaica, destroyed.

1909. In Sicily and southern Italy, Messina and many towns and villages desolated. Appalling loss of life; thousands buried alive; the survivors homeless; one of the greatest earthquakes of modern times if not of all time.