GeekMom Home Experiment: Can You Spot an Earthquake?

I have now experienced two earthquakes in my life, the first on July 16, 2010, the same morning my son was born, and again yesterday, August 23, 2011. I never thought that living on the East Coast that I’d ever rock the way that I did today. My two-year-old thought that he was on a roller coaster, and loved it. On the other hand, my heart was pounding for hours after the quake.

I know that I always love looking at the scientific data after an earthquake, especially looking at seismograph strips where you can see where the earth moved and each subsequent aftershock. A seismograph is an instrument used by seismologists (earthquake scientists) to record the strength or intensity of earthquakes. Seismologists use a seismograph recorded strip to determine the intensity of the initial quake (5.8 on the Richter scale) and its subsequent aftershocks. Seismologists can also gather more information from a seismograph than just intensity; they are trained to analyze all of the bumps and movements to determine what kind of tectonic movement caused the quake, whether it is a dip slip fault or a strike slip fault.

Building a home seismograph is pretty easy. (Not to mention it will give your kids something to do if school has been cancelled because of East Coast Quake 2011.)

Directions to make your seismograph:

Materials: scissors, shoebox with a lid, a heavy weight, masking tape, a pencil with an eraser, a weight for the pencil like nails or washers, Playdoh or clay, two paper clips, string and 2 (or more) sheets of paper.

1. Carefully cut a tiny slit in the middle near one end of the shoebox lid.
2. Place the open box upright, on one end, and put something small and heavy inside to keep it in position.
3. Tape the lid onto the top of the box forming an upside-down “L” with the slit in the lid facing away from the box.
4. Attach the weights to the pencil near the sharpened end, make sure not to cover the point. Tape the weights tightly to the pencil. A small piece of clay will keep the weights from slipping off. The weights must be fairly heavy so the seismograph recorder pencil will make good contact with the paper and draw fairly dark drag lines on it.
5. Open one end of a paper clip and push it securely into the eraser end of the pencil. Tie the string to the unopened end of the clip.
6. Attach the second paperclip to the other end of the string, and wind the string around the paperclip like you would wind kite string.
7. Slip the top clip through the slit and adjust the pencil marker so the tip rests on the table, not perfectly straight, but dragging as it moves.
8. Slip the remaining string under one side of the clasp to fasten the upright pencil into place.
9. Cut each sheet of paper into thirds lengthwise. These strips will act as your roll paper and record your “earthquake movements”.

Time to record an “earthquake”!

Place a paper strip against the box (below the slit you made in the lid) and slowly pull the strip forward.

• Notice how straight the drawn line is as you move the strip of paper.

Have someone else bump and shake the table as you pull the paper strips under the dragging pencil marker.

• Notice how your seismograph makes sideways and up and down movements.

Compare the separate strips of paper.

• How do the lines differ? how do they show the effects of movement? Could you learn to recognize the difference between a shake and a bump of the table?