Seismograph

You can record waves on your own seismograph. Since not all types of waves are passed through the earth, your model of the seismograph will show only those surface waves that move the ground up and down (ground roll) and waves that shift it back and forth (shearing). These are referred to as Rayleigh and Love waves.

Materials

General safety rules should be followed.

Using the string, suspend the weight over the edge of a table. Carefully attach a sharpened pencil to the side of the weight so that the lead of the pencil points towards the floor. (You can attached the pencil with tape or a rubber band.) The tip of the pencil should just clear, but not touch, the floor. Place the band of paper directly under the pencil. Practice pulling the paper under the pencil at a constant rate.

When you are ready to start your graphing, pull the paper strip and have your friends continuously pound on the table top on each side of the string for 15 seconds. Be sure that they hit the surface harder for a period of time. Observe the patterns created by the vibration of the desktop. Can you identify when the most intensive waves were being sent (received)? What motions can you identify on your graph? How are these similar to the surface waves from an earthquake?