Next to the violent shaking of the earth's crust, perhaps the most wonderful and impressive thing is the great variety of sounds and noises. These occur not only while the earth-waves are passing through the crust at any place, but also long before the principal shocks reach the place, as well as long after they have passed.
Earthquake sounds vary almost infinitely, both in intensity and character. Some are like the gentle sighings of the wind, or resemble faint mysterious whisperings; some are not unlike the confused murmurings of a crowded room; some resemble the sounds of a busy street. Some sounds are full and strong, like the deep bass notes of a large organ. Others resemble the din of a great battle with the reports of the large guns. Still others reach the intensity of continuous peals of thunder. But we can better understand the nature of earthquake sounds from an actual description of them in a number of great earthquakes, and by inquiring at the same time into any of the peculiar facts connected.
Humboldt in his great work, "Cosmos," thus describes the varied voice of the earthquake:
"It is either rolling or rustling, or clanking, like chains being moved, or like near thunder, or clear and ringing, as if obsidian or some other vitrified masses were struck in subterranean cavities."
That the sounds produced during earthquakes are carried through the ground faster than through the air appears clear from the fact that such sounds are sometimes heard in deep mines when they are not at all heard on the earth's surface.
In describing the earthquake that occurred in Kamtschatka, in 1759, Krashenikoff of St. Petersburg states that noises were heard like the rushing of a strong underground wind, accompanied by a hissing sound, which resembled the sizzlings heard when red hot coals are thrown in water.
In an earthquake that occurred in Lincolnshire, England, February 6th, 1817, a noise was heard closely resembling the sounds of wagons running away on a road. So complete and convincing was the resemblance that several wagoners on one of the roads drew their teams to one side so as to permit the runaway to pass safely.
Another kind of noise heard during earthquakes is a loud hollow bellowing. Sometimes, however, the sounds are more musical in their nature, being not unlike those produced by a very large organ pipe. At other times they resemble the noises produced when steam is blown into cold water.
The following account of earthquake sounds is given by Daubeny, in his book on volcanoes. It appears that during March, 1822, the people living on the island of Melida, opposite Ragusa, in Dalmatia, were greatly alarmed by sounds that at first they believed due to cannonading either at sea or on the neighboring coast. They afterwards found that these sounds were due to something that was taking place under the ground. The noises continued at intervals until August 23d, 1823, when a great earthquake occurred, during which one of the highest mountains on the island was cleft or split in one place. The underground noises continued from time to time and so frightened the people that they were about to leave the island permanently and emigrate to the mainland of Dalmatia. They were dissuaded from doing so by the government, and while the noises continued at intervals it so happened that no damage came to them. It is said, however, that twenty years after an active volcano broke out on the island.