Abstract

Objective

The goal of this science project is to build and test your own seismograph.

Introduction

A seismograph is an instrument that detects and records ground motion. Ground motion can be caused by something man-made, such as a mine blast or a nuclear explosion; or by natural events, such as landslides, volcanic activity, or most often, earthquakes. Whenever any of these events occur, seismic waves are created, and it is these waves that a seismograph picks up.

There are two main types of seismic waves: body waves, which can travel through the inner layers of the earth, and surface waves, which can only travel on the surface. Body waves are the fastest and have the highest frequency. The first type of body wave is called the primary or P-wave. It pushes and pulls the solid rock or liquid matter that it is moving through, and people feel it as back-and-forth or side-to-side motion. The second type of body wave that you feel in an earthquake is called the secondary or S-wave. S-waves cannot move through liquids, only through solid rock. They move rock particles perpendicular to the direction the wave is traveling in. Don’t miss the exciting wave animations in the bibliography where you can see body waves and surface waves in action on rock particles!

Click here to watch a video of this earthquake investigation, produced by DragonflyTV and presented by pbskidsgo.org.

Did you know you can see evidence of the power of seismic waves all around the San Francisco Bay area? Watch the DragonflyTV video and follow Claire and Nisha as they discover signs of earthquakes in the roads, buildings, and ground all around their neighborhood.

So how does a seismograph measure seismic waves? Imagine trying to draw a straight line on a piece of paper while someone is holding your elbow and jiggling it back and forth. It would be hard to get the line straight, wouldn't it? A simple seismograph is kind of like your arm holding a pen. A horizontal beam (like your arm) holds the pen. The "elbow" end of the rod (the stand) is connected firmly to a sturdy vertical post (see the diagram below). To keep the beam from moving from small vibrations, a heavy weight is attached to the beam. The pen writes on paper mounted on a roll, which is turned at a constant speed (either by hand, or with a motor). Shaking of the ground causes the vertical stand to move up and down. This, in turn, causes the horizontal beam to jiggle back and forth. So instead of a straight line on the paper, the pen makes back-and-forth motions to draw squiggly lines. The greater the vibration, the greater the height of the squiggles, meaning the greater the intensity of the seismic waves.

This is a diagram of a homemade seismograph. (UC Regents, 1995.)

The lines drawn by the seismograph result in what is called a seismogram. In this science project, you will build your own seismograph and see how well it can record ground vibrations.

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• Seismograph
• Earthquake
• Seismic wave
• Body wave
• Surface wave
• Frequency
• Primary wave (P-wave)
• Secondary wave (S-wave)
• Fault
• Tectonic plate
• Seismology

Questions

• Can your seismograph detect vibrations from someone jumping up and down nearby?

Bibliography

• TPT. (2007). Earthquakes by Claire and Nisha. DragonflyTV, Twin Cities Public Television. Retrieved May 5, 2008 from http://kids.pbs.org/dragonflytv/show/earthquakes.html
• UC Regents. (1995). Building Your Own Seismograph. Retrieved December 20, 2006 from the Regents of the University of California Center for Science Education, Space Science Laboratory at UC Berkeley's website: http://cse.ssl.berkeley.edu/lessons/indiv/davis/hs/Seismograph.html
• For getting started on your background research, here are two good references on seismology:
  
  • Wood, M.M. and Pennington, W. (2006). UPSeis, an Educational Site for Budding Seismologists. Retrieved December 20, 2006 from the Department of Geological and Engineering Sciences, Michigan Technical University's website: http://www.geo.mtu.edu/UPSeis/index.html
  • Wikipedia Contributors. (2006). Seismology. Wikipedia: The Free Encyclopedia. Retrieved December 20, 2006 from http://en.wikipedia.org/w/index.php?title=Seismology&oldid=96601497
• Here are some good resources on earthquakes and their effects:
  UC Regents. (1999). Earthquakes and Their Effects. Retrieved December 20, 2006 from the UC Berkeley Seismological Laboratory's website: http://seismo.berkeley.edu/seismo/resource/teaching.html#eq
• For some sample seismograms from a state-of-the art seismograph, see:
  UC Regents. (2005). Seismograms of Interest. Retrieved December 20, 2006 from the Northern California Earthquake Data Center, University of California, Berkeley and USGS's website: http://www.ncedc.org/bdsn/seismograms_of_interest.html
• On this webpage, you can make your own seismogram from historic data:
  UC Regents. (2005). Make Your Own Seismogram! Retrieved December 20, 2006 from the Northern California Earthquake Data Center, University of California, Berkeley and USGS's website: http://www.ncedc.org/bdsn/make_seismogram.html
• This source displays animations of body and surfaces waves.
  Michigan Technical University. (2007). What is Seismology and What Are Seismic Waves? UPSeis, an Educational Site for Budding Seismologists. Retrieved May 5, 2008 from http://www.geo.mtu.edu/UPSeis/waves.html

Materials and Equipment

To do this science project you will need the following materials and equipment:

• Wood base, 10" x 24" x 0.5"
• Wood stand, 2" x 4" x 12"
• Wood support blocks, approximately 2" x 4" x 8" (2)
• Wood beam, 1" x 1" x 20"
• Wood dowels, diameter = 0.25", length = 10"; one dowel must slide through center of adding machine paper roll (2)
• Brick or other compact heavy weight
• Strong wire or non-elastic thick rope or twine (7 feet total)
• Roll of adding machine paper, width >= 2"
• Smooth-sided can with lid and base (similar dimensions as paper roll)
• Round-headed screw, or bolt or nail; 1" long
• Pen
• Various sizes of nails
• Strong tape (masking, strapping, or duct) for attaching weight
• Lab notebook

Shop for Supplies at Science Buddies Online Store

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Experimental Procedure

Building the Seismograph

1. Build the seismograph according to the diagram below.

   This is a diagram of a homemade seismograph. (UC Regents, 1995.)

2. Here are some important steps and/or modifications you may need to consider:
   1. If you have a drill, you can mount the two wood dowels in holes drilled through the two wood support blocks. If you do not have a drill, saw two slots into the upper edge of each wood support block and then drop the dowel into these slots.
   2. The pen must write easily when pulled down onto the paper roll by the brick. Cap it when not in use. You may try substituting a soft lead pencil, a charcoal pencil, a crayon, etc.
   3. Fasten the wood stand securely to the wood base by nailing upward from underneath the wood base. The wire (or cord) attached to the back and side of the wood stand will help to keep it stable.
   4. Fasten the screw securely into one end of the wood beam. This screw will rest against the wood stand so that the wood beam hangs level over the base. To help the screw stay in place and not slip off of the wood stand, drill or carve a small hole 1/4-inch deep out of the stand and slightly larger in diameter than the screw head. The head of the screw can sit in this hole and press against the wood stand.
   5. Both the adding machine paper roll and the smooth can should be able to rotate. The smooth can rotates when you crank the nail at one end of its wood dowel; the paper roll can turn either with its wood dowel or separately from the dowel. Tape down the end of the paper roll onto the can so that when you crank the can, the paper should wind up around the can and cause the paper roll to rotate as it feeds paper to the can.
   6. If you want to be creative, see if you can devise a way to make the paper roll feed onto the smooth can automatically so that you do not have to crank the can by hand. You might try buying a miniature battery-operated motor that can turn the wood dowel of the can.

Testing the Seismograph

Here are some ideas for testing the seismograph. You can probably think of other ideas on your own.

1. Have a helper jump up and down on the floor near the seismograph.
   1. How does the seismogram change as the jumping person moves farther away. Make measurements with the person at a distance of 0.5, 1, 2, 4, 8, and 16 meters away from the seismograph. Make a graph of seismogram peak height (in cm, y-axis) vs. distance of your helper from the seismograph (in m, x-axis). You could also use the seismograms themselves on your display board.
   2. How does the seismogram change if the person jumping is heavier or lighter? Pick a distance from your first experiment where the pen moved noticeably, but did not cover its full range of motion on the paper. Make a series of seismograms with helpers of different weights jumping up and down at that fixed distance from the seismograph.
   3. How does the seismogram change when you vary the substrate on which it is standing? For example, compare placing the seismogram on a wooden floor vs. a concrete slab (like your garage floor), or on a table vs. directly on the floor, or on your lawn vs. a hard-surfaced playground.
2. Safety note: adult supervision required for outdoor measurements near traffic. You could also try your seismograph at different locations outdoors. For example, if you place the seismograph on a sidewalk, can you see vibrations from nearby foot or vehicle traffic? Can you identify when larger vehicles, such as trucks or buses, pass by?

Variations

• What do you think will happen if you use a lighter weight on the horizontal rod of your seismograph? If you use a heavier weight?
• Another way to test the seismograph would be to drop a box containing objects with increasing mass at different distances from the seismograph. For example, you could use 20-pound sacks of dry rice, or an increasing number of books. Use a bathroom scale to measure the weight of the box. You can also try this test on different substrates (wood floor vs. concrete slab).
• Advanced: Can you think of ways to improve the seismograph? Or can you think of different way to measure seismic waves? Draw a clear diagram that shows and labels all parts. Then write a paragraph explaining how your design works. Here are some important considerations as you are coming up with your design:
  • Is it made of common inexpensive materials found in a local store?
  • Will it be able to determine the relative magnitude (size) of each vibration it measures?
  • Will it be able to measure vibrations continuously for at least 1 minute?
  • Will it be able to measure even slight vibrations (such as a person jumping up and down next to your seismograph)?
  Gather the materials you need and build the seismograph you designed. Be prepared to show other students how your device works (UC Regents, 1995).
• For a project using data from state-of-the art seismographs that you can access online, see the Science Buddies project How Fast Do Seismic Waves Travel?
• For a more advanced project that uses seismometer data, try the Science Buddies project Locating the Epicenter of an Earthquake.

• For more science project ideas in this area of science, see Geology Project Ideas.

Credits

Sources

This project is from:

• UC Regents. (1995). Building Your Own Seismograph. Retrieved December 20, 2006 from the Regents of the University of California Center for Science Education, Space Science Laboratory at UC Berkeley's website: http://cse.ssl.berkeley.edu/lessons/indiv/davis/hs/Seismograph.html

Edited by Andrew Olson, PhD, Science Buddies

Last edit date: 2008-06-18 12:00:00