This activity uses software called Seismic Waves: A program for the visualization of wave propagation to illustrate how waves from an earthquake travel to seismic stations throughout the earth.

What do seismic waves reveal about earth’s interior structure?

Go to http://www.geol.binghamton.edu/faculty/jones/

Scroll halfway down the page and look for the following link: SeismicWavesSetup.exe. Click on that link and the software will download to your desktop.

NOTE: Seismic Waves software runs on Windows machines only.

This activity addresses NSES standards for earth and space science and inquiry at grades 5-8 for structure of the earth system.

1. Click the Seismic Wave Maintenance icon on your desktop.
2. Go to the Preference Menu select Time to Pause at end… A dialog box will appear. Type as many 9s in the box as you can.
   
3. Close the Maintenance program.

Do all earthquake seismic waves travel at the same speed through earth? Explain your prediction.

1. Click the Seismic Waves icon on your desktop.
2. Select View under the Options menu. Select Earth.
3. Click the Start button. A new window will open.
4. Click on the Northridge earthquake of 1994. Your screen should show a large 3-dimensional view of the earth with P and S waves traveling across the surface.
5. Which waves travel faster along the surface of earth — P waves or S waves?

6. P waves move in a compressional motion like a slinky where s waves move up and down like when you wave a rope up and down. Click this link to see a view of how these waves travel: http://www.thetech.com/exhibits_events/online/quakes/waves/p&s_waves.html.
7. Now you are going to observe how seismic waves travel through earth. Select View under the Options menu. Select Cross-section.
8. Click the Repeat button in the menu on the right side of the screen.
9. Watch how the P waves (red) and S waves (blue) travel through earth.
10. Note when the waves go through each layer of earth they are given a new label: K is for the outer core and I is for the inner core. So a seismic wave labeled PKIK, for example, has traveled through the outer core, the inner core, and then the outer core again.
11. Click the Repeat button one more time. This time click the Pause button when the timer says 5 minutes. (The timer is a box on the right side of the screen.)

12. Click the Resume button and once again click the Pause button when the timer reads 10 minutes.

• Which waves travel fastest through the mantle?
• Describe what happens when the first P wave hits the boundary of the outer core.
• Describe what happens when the first S wave hits the boundary of the outer core.
• What types of waves make it to the opposite side of the earth (relative to the location of this earthquake)?

Take a few moments to respond to the following: What can seismic waves tell you about earth’s interior structure? Are all the layers the same? How do you know?