LESSON FOUR

How do we get the magnitude and epicenter of an earthquake? (one class period)

[For the Teacher]:
Distribute the journals. Discuss seismograms and seismometers. Point out that different seismic waves make different patterns. P waves look jittery with no pattern of peaks and valleys; S waves make recognizable patterns of peaks and valleys. P waves are compression waves whereas S waves are shear waves going sideways. Have examples to show them. Next, have students access the Electronic Desktop Project: Virtual Earthquake (http://vquake.calstatela.edu/eec/Earthquake/) site.

Groups can be together but it is better that each member of the group has his/her own computer. The site will ask him/her to choose an earthquake location. The site will post seismograms of a past earthquake at that location. Virtual Earthquake will teach students how to measure earthquake travel time and wave amplitude on the seismograms. All students are given more than one chance to get it right. The site will show students how to use seismogram measurements to calculate magnitude using a Richter nomogram and how to triangulate three seismograms to find the earthquake's epicenter. After completion of the exercises, students are issued certificates of completion that can be saved as GIF images and printed later for their journals.

How do we calculate the magnitude of an earthquake and locate its epicenter?

[For the Students]:

Your teacher will give you a short lesson on seismograms. They are produced on seismometers, which record earthquake waves. P or primary waves are compression waves and are seen on the seismogram as jittery peaks with no pattern of valleys. S or secondary waves are shear waves and they record back and forth motions. They have a definite pattern of peaks and valleys and can be quite large.

When instructed, go to the Electronic Desktop Project: Virtual Earthquake (http://vquake.calstatela.edu) site. The site will teach you how to use a seismogram to find the magnitude and epicenter location of a local earthquake (within 500 miles). Remember to take notes in your journal.

When you are finished, the site will give you a certificate of completion. Ask your teacher if you can print it now or save it for printing later.