Earthquake can be defined as a sudden jolt or tremor given to the earth by some interior disorder in a volcano. Many earthquakes are so gentle as to pass almost unrecognized, other are sufficiently pronounced to excite general alarm, while some spread enormous destruction. Destructive earthquakes are usually confined to limited regions. The usual phenomena recorded in well-known earthquakes are first a trembling,
next one or more severe shocks, and then a trembling which gradually dies away. In most cases, each shock lasts only a few seconds, but the trembling that follows may continue for days, weeks, or even months.
Noises of various kinds usually accompany an earthquake. They have been likened to the howling of the storm, the growing of thunder, the clanking and clashing of iron chains, or the rumbling of heavy wagons along a road.
Such noises are conducted through the ground, or they may travel through the sea or air, and are often heard at great distances from the place where the shock is felt.
