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# Long Enough: What Effect does the Duration of an Earthquake Have on the Land Surface?

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Source:
Author: Janice VanCleave

### Problem

What effect does the duration of an earthquake have on the land surface?

### Materials

• Large shoe box
• Unpopped kernels of popcorn
• Timer
• Metal spoon

### Procedure

1. Turn the box upside down on top of a table.
2. Cover the roof of the inverted box with a layer of popcorn kernels.
3. Hold the box steady with one hand.
4. Set the timer for 5 seconds.
5. Immediately start gently tapping the spoon on the side of the box just below the top edge.
6. Observe the movement of the kernels as you tap.
7. Stop tapping at the end of 5 seconds.
8. Set the timer for 10 seconds, and repeat the experiment.
9. Observe the movement of the kernels again as you gently tap the side of the box.

### Results

Tapping the box causes the popcorn kernels to vibrate. Those kernels near the edge fall off the box, while the ones farther from the edge move only slightly. Increasing the time duration of the tapping causes more kernels to move farther away from their original position.

### Why?

The longer the duration of an earthquake, the greater is the total amount of energy received by the affected area, which results in more damage. The duration of an earthquake is related to the amount of shaking energy released by the quake. Shaking energy is referred to as the magnitude of the earthquake and is measured by the Richter scale which ranges from 1 to 9. There is no absolute time of duration for earthquakes, but, generally, quakes with moderate shaking energy (magnitude up to 6) last from 5 to 10 seconds. Major quakes (magnitude of 6.5 to 7.5) last 15 to 30 seconds, while great quakes (magnitude of 7.75 or more) last for 30 to 60 seconds.

### Let's Explore

1. Gentle tapping for 5 to 10 seconds represents the magnitude and duration of a moderate earthquake. Represent a major earthquake by repeating the experiment twice, first tapping harder for 15 seconds, and then tapping even harder for 30 seconds. Science Fair Hint: Compare the number of popcorn kernels that fall off the box with the different magnitudes and time durations.
2. How would a different ground cover be affected by the vibrations? Cover the box with dirt, and repeat the experiment. (perform the experiment outside, or use a tray to collect falling dirt.) Science Fair Hint: Pictures of the surface of the box before and after tapping on the box's side can be used as part of a science fair display. Label each diagram with the time in order of least to greatest duration.

### Show Time!

How are structures affected by the duration of an earthquake? Use dominoes or wooden blocks to construct "houses" about 12 inches (30 cm) from the edge of a table. Use your fist to gently hit the table nearest the houses for 10 seconds. Observe any change in the structures of the houses. Repair any damage to the houses, and then repeat by hitting the table with the same force for 30 seconds. Use photographs of the houses, before and after vibrating the table, as part of your project display.

### Check It Out!

Earthquakes usually last for a short duration of from 10 to 60 seconds. Read about different recorded earthquakes, and make a chart dividing them into categories of great, major, and moderate quakes.

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