chart of earthquake

When we think of an earthquake, we think of buildings toppling, huge cracks opening up in the earth, and so on. What is there to be “measured?” Well, an earthquake is a trembling or vibration of the earth’s surface. And it iS these vibrations that are measured. The cause of an earthquake is usually a “fault” in the rocks of the earth’s crust, a break along which one rock mass has rubbed on another with very great force and friction. Much of the vast energy in this rubbing is changed to vibration in the rocks. This vibration may travel thousands of miles, which is why an earthquake in Tokyo can be detected and measured in England.