LESSON THREE
How are earthquakes measured? (one class period)
[For the Teacher]:
Distribute the journals. Break students up into groups again. Ask them to brainstorm how they would measure an earthquake. Have groups report their ideas. Next, have them access the site Earthquakes: The Richter Scale (http://www.zephryus.demon.co.uk/education/geog/tectonics/richt.html). Groups should note how the Richter and Mercalli scales are used and the advantages and disadvantages of each. After viewing the site, have groups report on the two scales and how they are used. Point out that the Richter scale is a logarithmic scale and that each increase of one is a tenfold increase in energy.
Discuss logarithms and how they are used. Students should know that the natural logarithm of 10 is 1, of 100 is 2, and so on. Ask them what the log of 50 would be? The question could be framed as follows:
10^{
1}=10
10^{
2}=100
10^{
?} = 50 (between one and two)
Show students how to get natural logarithms on a scientific calculator. After discussing logarithms, ask groups to report on the advantages and disadvantages of each scale.
How are earthquakes measured?
[For the Students]:
Discuss with your group how you would measure an earthquake. Don't forget to write in your journal.
After group reports, go to the Earthquakes: The Richter Scale (http://www.zephryus.demon.co.uk/education/geog/tectonics/richt.html) site and take notes on how the Richter and Mercalli scales are set up, and how they are used. Write a paragraph on the advantages and disadvantages of each scale.
When finished, group reports on the Richter and Mercalli scales will be given.
Next, your teacher will give you a short lesson on logarithms. Remember that logarithms are exponents. Natural logarithms use a base of 10. Scientific calculators have a log button that gives the natural logarithm of positive numbers.
After the minilesson, group reports will be given on the advantages and disadvantages of both scales.
