How to Build a Simple Seismograph to Detect Earthquakes

Learn to build an easy seismograph with your kids using household materials to detect and measure ground movement.

1. Gather Your Materials. You'll need a cardboard box (shoebox size works perfectly), a piece of string about 12 inches long, a marker or felt-tip pen, a small weight like a rock or large washer, tape, a long strip of paper, and scissors. Most families have these items lying around the house, making this an accessible project for everyone.
2. Set Up the Box Base. Turn your cardboard box upside down so the opening faces the ground. This creates a stable platform for your seismograph. Cut a small hole in the top center of the box, just big enough for your marker to fit through. Make sure the hole is smooth so the marker can move freely without getting stuck.
3. Create the Pendulum. Tie one end of your string securely to the marker and the other end to your weight. The string should be long enough so that when the weight hangs down, the marker tip just touches the surface where you'll place your paper. Test the length by holding the string above the box and adjusting until the marker barely touches the top of the box.
4. Install the Detection System. Thread the string through the hole in the box so the weight hangs inside the box and the marker hangs outside. Tape the string firmly to the inside top of the box, making sure the marker can swing freely. The weight acts as a stabilizer, so when the ground moves, the box moves but the hanging marker stays relatively still.
5. Add the Recording Paper. Place a long strip of paper under the marker. You can tape several pieces together to make it longer, or use a roll of paper if you have one. The paper should be positioned so the marker tip will draw on it when the seismograph detects movement. Make sure the paper can be pulled slowly and steadily across the marker.
6. Test Your Seismograph. Have someone slowly pull the paper strip under the marker while another person gently shakes the table or stomps nearby. You should see wavy lines appear on the paper as the box moves but the marker stays steady. The bigger the vibration, the bigger the waves on your paper. Try different types of movement to see how your seismograph responds.
7. Understanding Your Results. The lines your seismograph draws represent ground movement. Straight lines mean no vibration, while wavy lines show movement. Bigger waves indicate stronger vibrations, and the frequency of the waves shows how fast the ground moved. Real seismographs work on the same principle but are much more sensitive and precise.