A seismic science activity from Science Buddies

Key Concepts Physics Engineering Earthquakes Measurement

Introduction Scientists study earthquakes so we can understand and predict them better. In this activity you will learn about one of the tools scientists use to measure the strength of an earthquake—and build your own machine using simple materials.

Background Earthquakes happen all the time, but most of them are so small that we can't feel them, and they don't cause any damage. Large earthquakes, however, can be catastrophic—causing significant damage to property and loss of life. An earthquake's strength is measured on what is called the Richter scale. The Richter scale goes from 1 to 10. Each increase of 1 on the Richter scale means the earthquake is actually 10 times more powerful (for example a 2.0 earthquake is 10 times stronger than a 1.0 earthquake—not twice as strong). As of 2019 the strongest earthquake ever recorded measured 9.5 on the Richter scale.

Scientists use a machine called a seismograph to measure the motion of the ground during an earthquake. Seismographs are very sensitive and can detect earthquakes that occur very far away (along with other things that make the ground shake, such as volcanic eruptions or large explosions) that might be too faint for humans to feel. Seismographs are made by hanging a heavy weight from a rigid frame connected to the ground. When the ground moves during an earthquake, the frame moves back and forth along with the ground. The heavy weight, however, is not connected directly to the ground, and it wants to stay in place. The result is that the weight holds still, while the frame moves back and forth around it. By placing a pen on the weight and paper on the frame scientists can see the relative motion of the weight and frame through the markings, which create a seismogram. The seismogram can be analyzed later to find out when an earthquake happened and how strong it was. Modern seismographs record this motion as an electrical signal, but in this activity you will build your own old-fashioned seismograph that uses a marker to record an "earthquake" on a paper strip.

Observations and Results When your helper pulls the paper through the box with no shaking the marker should just draw a straight line on the paper. When you shake the box, it moves back and forth, and the paper moves along with it. Because of the heavy mass of the cup and the way it is suspended by strings, the cup does not move as much. This means that the paper moves back and forth under the (mostly) stationary marker, resulting in a squiggly line. The size of these squiggles (called their amplitude) corresponds to how hard you shook the box—just like how the line drawn by a real seismograph corresponds to the strength of the earthquake.

More to Explore Seismographs, from Incorporated Research Institutions for Seismology Global Seismographic Network, from USGS Earthquake-Proof Engineering for Skyscrapers, from Scientific American Earthquake Rollers, from Scientific American STEM Activities for Kids, from Science Buddies

This activity brought to you in partnership with Science Buddies

Ben Finio is a senior staff scientist at Science Buddies and a lecturer at the Cornell University Sibley School of Mechanical and Aerospace Engineering. Follow him on Twitter @BenFinio.

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