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What is a Seismograph?

Earthquakes are fascinating and frightening at the same time. Have you ever wondered how scientists study these earth-shaking events? They use what's called a seismograph, also called a seismometer, which is an instrument that measures and records seismic waves that move through the earth as the result of an earthquake.

A modern seismograph can help scientists detect earthquakes and measure several aspects of the event:

• The time at which the earthquake occurred
• The epicenter, which is the location on the surface of the earth below which the earthquake occurred
• The depth below the earth's surface at which the earthquake occurred
• The amount of energy released by the earthquake

Scientists measure and record this data to learn more about earthquakes, tectonic plates, and Earth's layers. Earthquakes are difficult to predict, but scientists studying them hope to use seismographic measurements to be able to make more accurate predictions.

The idea behind a seismograph is fairly simple. A basic seismograph includes a solid base and a heavy weight suspended from a spring over the base. A pen hangs from the weight and a rotating drum with paper sits below it on the base. The tip of the pen touches the drum. When the earth shakes from an earthquake, the drum rotates and the weighted pen moves back and forth due to the motion of seismic waves. The pen records the movement on the drum. The paper recording of an earthquake is called a seismogram.

The most high-tech seismographs used by scientists studying earthquakes today are sophisticated and precise. They are based on the same concept as a basic, simple seismograph, but make use of electronics, magnets, and amplifiers in order to accurately and precisely measure the smallest ripples in the earth caused by earthquakes.

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[Michael Shermer]

Science is the best tool ever devised

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