Seismic Eruption Tutorial: A Closer Look

By Amy Pallant, apallant@concord.org

The Concord Consortium

Launching the Seismic Eruption Software

1. Click the Seismic Eruption icon (not the Smithsonian version) on your desktop.

2. Click Go.

3. Go to the Control Menu and select “Global Audio.” Uncheck it if you would like to turn the sound off.

4. Click the World button in the center of the screen to run a view of all the earthquakes that have occurred in the world between January 1, 1960, and the present time. The simulation will begin automatically.

5. Speed up the program to 6 months per second by clicking the up arrows on the speed control below the map or by going to the Control Menu, selecting the speed menu and changing the speed.

6. Go to the Control Menu, select Time to Pause at end….

The following dialog box will appear:

Type as many 9s in the box as you can.

7. Observe the earthquakes for a few minutes. If you’d like, click the Pause button. To restart the software, click the Repeat button.

Locating different maps using Seismic Eruption

1. Launch the Seismic Eruption program if it is not open already.

2. Select a different map view by going to the File menu, selecting “Open View,” and scrolling down to location you would like. Choose Atlantic, for example, then click OK. You will see a map with the Atlantic Ocean in the center.

3. Click the Plates button (lower right) to see plate boundaries. Click the Key button (upper right) to read descriptions of the plate boundaries.

Change EQ Cutoff

1. In the key below the map, set the EQ Cutoff number to seven (7), so that only earthquakes greater than or equal to 7 in magnitude are displayed on the map.

2. Click the Repeat button to start the simulation again.

3. If you change the earthquake magnitude to display earthquakes below magnitude four (4), you will need to change the scale. Go to the Earthquakes menu, select “Magnitude/Depth scale” and adjust the scale to reflect your changes.

4. Click the Repeat button below the map. Allow the program to run from 1960 to the present.

Constructing a Cross-Section

Geologists like to analyze problems (such as the geologic history of an area, the layers and patterns of rocks below the earth’s surface, or the movements of plates on earth) by constructing cross-sectional views. They do this by drawing a line through a portion of a map. In other words, if you could slice through a portion of earth, pull away one half, and look at it from the side, you would be able to see what is going on below the surface.

Imagine you had a frosted cake and you were asked the following two questions: How many layers does the cake have and what are the layers made of? How would you tell? You wouldn’t be able to answer without cutting the cake and looking at the cake from the side.

The Seismic Eruption software allows you to create a cross-section and view the locations of the epicenters of the earthquakes below the earth’s surface. It is a different way to visualize the data. In this case, the software creates a graph where the top of the graph represents earth’s surface and the side of the graph represents kilometers below the surface.

1. Launch the Seismic Eruption program if it is not open already.

2. Go to the world view by clicking the World button in the middle of the screen.

3. Go to the Control Menu and select “Set up Cross-Section view.” (You will create a cross-section by creating a square around the area on the surface map where you want to view a cross-section. You may like to allow the program to run for a few minutes to determine a place of interest.)

4. The following dialog box will pop up. In the example below, the settings are 5 degrees azimuth, and a geographical area 100 kilometers long and 100 kilometers wide.

5. Begin by clicking anywhere on the map. This will cause an icon like the one below to appear on your screen.

6. You can leave the icon in the location you clicked or you can move it to by clicking and dragging the icon to a new location.

7. Change the length of the box. Increase the number in the window to 1500 km by using the arrows or typing in new numbers.

8. Click the Redraw button (not the OK button) and watch what happens to the icon.

9. Increase the width number in the window to 500 km by using the arrows or typing in new numbers.

10. Click the Redraw button and watch what happens to the icon on the map.

11. Now change the azimuth. (The azimuth is the horizontal angular distance from a reference direction, so it will change how the red line is drawn in comparison to the bottom of the screen.) Change the azimuth numbers by clicking on the arrows or typing in numbers. Click Redraw each time you make a change.

Azimuth set at the following:

-20 0 20 40

Mid-Atlantic ridge with cross section icon

12. Place the cross-section tool anywhere along the Mid-Atlantic Ridge. Be sure to place the azimuth so that it is perpendicular (a ninety-degree angle) relative to the plate boundary and crosses over the plate boundary. Ideally you want the boundary to be approximately in the center of icon.

You must be very careful to place your mouse where you want the cross-section tool to cross the boundary. This should be where the earthquakes are located. See how the tool crosses the boundary in the image, above.

After you have placed your tool across a boundary, click the Plates button again to ensure you have the tool where you want it.

13. Click the OK button to save this information.

14. View the cross-section by going to the Control Menu, selecting “Mapview/3-D/Cross-Section,” and clicking the “Cross-Section View.”

Below is a picture of a cross-section of the Mid-Atlantic Ridge. The cross section’s x-axis represents width and the y-axis represents its depth. In the example, the width is 1500 kilometers and the image shows depths to 500 kilometers below the surface.

In this view you can see the depth of earthquakes that have occurred over the last 50 or so years by looking at the circles. If a circle is plotted over another circle, the epicenters were at the same depth and in the same location, but occurred at different times.

15. To return to map view, go to the Control Menu, select “Mapview/3-D/Cross-Section,” and click “Map View.”