On September 1st, 1923, an Earthquake struck the city of Tokyo. Houses collapsed and cooking fires set the wreckage ablaze.

Families took refuge in a public square. While they were huddled there, a wind swept the fire over them and their possessions, killing thousands.

The very instruments for recording earthquakes were knocked out of operation. Scientists stayed at their stations and set them running again.

Not knowing whether their own families were alive or dead, they worked to save the records so valuable to the nation and the world. Such records may lead o ways of predicting in time and reach places of safety.

Vibration Waves:

The science of Earthquake is called seismology, from the Greek word Seismos, Earthquake.

The main instrument used for studying Earthquakes, the seismograph, records vibrations sent through the Earth shocks.

You can observe similar vibrations in a steel rod. Lay the rod down and place a ping pong ball against one end. Notice how the ball bobbles and rattles against the rod.

When you strike it, the steel at the end of the rod is compressed. Then, being springy, or elastic, it quickly jumps back.

By this movement the steel in the neighboring section is compressed, and it, too, rebounds. Thus, the compression and rebound are passed through the rod.

Meanwhile, the first section again compresses and jumps back. So does every other section.

As a result, a whole series of compressions travel through the rod. Another type of wave can be set off by striking the rod on the side.

A section of the steel is knocked sideways, them jumps back. This shakes the neighboring section, which shakes the next, and so a wave of shaking motion travels through the rod from end to end.

Portrait of an Earthquake