The San Francisco Treat
Introduction
Use Spaghetti to illustrate the earthquake magnitude scale.
Material
A package of thin spaghetti, 0.5 kg or one pound
To Do and Notice
Hold up one piece of spaghetti.
Bend the piece between your hands until it breaks.
Notice the work it takes to break the spaghetti.
Call this a 5 on the pasta magnitude scale.
Hold up a bundle of 30 pieces of spaghetti.
Bend the bundle until it breaks.
Notice the work it takes to break the bundle.
If the pasta magnitude scale were like the earthquake magnitude scale
this would be a Pasta magnitude 6 break.
Hold up 900 pieces of pasta, the remainder of the
package.
Bend the bundle until it breaks.
Notice the work it takes to break the bundle.
This is a Pasta magnitude 7 break.
What's Going On?
The magnitude scales for earthquakes are logarithmic scales.
In particular for the Richter scale, each increase of 1 unit on the scale, say from 6 to 7, represented an increase of one order of magnitude, i.e. times 10, in the amount of ground motion recorded on a particular type of seismograph.
More modern scales were defined to roughly agree with the Richter scale. One of these scales is the moment magnitude scale. In the moment magnitude scale an increase of one unit corresponds to a factor of 30 increase in the energy released by the breaking of the fault in an earthquake. That's why we increased the number of spaghetti noodles from 1 to 30 to 900 = 30 x 30.
To relieve the energy stored in one Pasta magnitude 7 you have to have 30 pasta magnitude 6 breaks!
So What?
In order to release the energy of one magnitude 7 earthquake you would have to have 30 magnitude 6 quakes or 900 magnitude 5's. So the energy of a big quake cannot be released through smaller quakes.
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Scientific Explorations with Paul Doherty |
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11 Nov 99 |