Waves and the Earth's Internal Structure

Using the program "Seismic Waves" to study the Earth's Interior

Part 1: A 3 dimensional view

Computer Steps:

1. Open the Accessories group.

2. Start the program Seismic Waves, by double clicking on it's icon.

3. Select View under the Options menu. Select 3-Dimensional and click OK.

4. Select Map under the Earthquake menu.

5. Click on the Northridge earthquake of 1994. If everything has worked out your screen should show a large 3-Dimensional view of the Earth with P and S waves traveling across the surface.

Questions:

1. How long does it take for the P wave to reach the edge of South America? _________

2. How long does it take for the S wave to reach the edge of South America? _________

Note that you can make it go in reverse using the speed adjuster and that you can restart it selecting Restart under Options

3. From what you observe explain how scientists can tell how far away an earthquake is from their recording station.

4. What do scientists actually measure to determine an earthquake's location?

Part 2: A Cross Sectional View

Computer Steps:

1. Select View under the Options menu. Select Cross Section and click OK.

2. Select Phases (which are wave types) under the Options menu. De-select all phases except the P and the S wave, then click OK.

3. Select Restart under Option.

Questions:

1. How long does it take for the P wave to reach the edge of the outer core? _________

2. How long does it take for the S wave to reach the edge of the outer core? _________

Again: Note that you can make it go in reverse using the speed adjuster and that you can restart it selecting Restart under Options

3. Select Phases again and click on the Help button. You will see useful information on phases and a description of each of the types of phases. From the descriptions answer the following question:

4. What happens that creates a pP wave?

5. What happens that creates a PcP wave?

6. From the descriptions predict what kind of wave or waves would travel all the way to the opposite side of the earth? __________

7. Reset the phase to include the one you selected and restart the event. Was your prediction correct? ________ If not, try again.

The following question will require you to select the phases that provide the best answer.

8. Reset the phases to include all possible phases. What types of waves make it to the opposite side of the Earth, (relative to the location of this earthquake)?

9. What areas of the Earth receive no type of P wave?

10. What areas of the Earth receive no type of S wave?

11. What types of waves do not travel through the outer core?

Part 3: 3 views together, including a seismograph.

Computer Steps:

1. Select View under the Options menu. Select All Three and click OK.

2. Select Phases under the Options menu. De-select all phases except the P and the S wave, the click OK

3. Select Restart under Option.

Questions:

1. What is the meaning of the codes on the side of the seismograph? (CCM-Z, COL-Z HRV-Z, ect.)

2. How could a seismologist tell the difference from a P wave and an S wave from the record. In other words, how do they look different?

3. According to the seismograph, how much time after the P wave arrives does the S wave arrive at COL-Z.

4. How does the time difference vary at recording stations farther away?