SO461, Geological Oceanography

Plate Tectonics GIS--Earthquakes & Volcanoes

Fall 2003


  1. Understand where shield  volcanoes and stratovolcanoes occur.
  2. Describe why earthquake databases have few records of very large or very small quakes.
  3. Discuss why both Ms and Mb scales exist for earthquakes.


We will use the MICRODEM computer progam. To start it, use the "Start, Programs, MICRODEM_TerraBase II ver 5" menu choice, and then pick the MICRODEM icon. You should have version 14.38.21 (or higher).  If not, you need to download the new version.

Within MICRODEM, if you have questions on GIS operations, check the help file. Learning to use a GIS is an important auxiallary goal of this lab. You should run through the tutorial, "Global Tectonics and GIS", available on the table of contents in the help file.

You should use two different base maps:

  1. The Smith & Sandwell predicted topography.
  2. A plain vector map.

We have the following GIS data layers for plate tectonics. They will be in c:\mapdata\database

Earthquakes (this will not be turned in, but designed to test your understanding of the GIS program and some key facts you should take from this lab):

Complete the following table:

Data Set Largest Magnitude Location and Likely Plate Setting
World earthquakes    
Significant US earthquakes    
South American Earthquakes    


Using the Harvard Centroids, get a scatter plot of the earthquake magnitude Mb versus Ms. Which is generally larger?


Using the Harvard Centroids, get histograms of the earthquake distribution by magnitude (either Mb or Ms). What is the shape of the distribution, and how can you explain what happens at both large and small magnitudes?  How does the number of quakes drop off with each increase in the magnitude scale?


Using the world earthquakes, where do the magnitude 8 earthquakes occur?


Using the Harvard Centroids, where do the magnitude 8 earthquakes occur and what are their focal mechanisms? You will have to look at the beach balls, as the simple classification fails for most of these. Does this follow from the locations in terms of plate boundaries.

Volcanoes (this will not be turned in, but designed to test your understanding of the GIS program and some key facts you should take from this lab):

How may stratovolcanoes are there in the world? (Be careful; check to see how consistent the Smithsonian was in coding the volcano type). Where are they located?


How many shield volcanoes are there in the world? Where are they located?


What type of volcano is Congo’s Mount Nyiragongo, erupting last year during this lab? What is its plate setting, and which other data sets can you use to check on this setting?


Assignment, for grade, done in teams of two:

Using the computer, recreate the map that you tried to create last week. Show the plate boundaries in your assigned area, and how they relate to earthquakes and volcanoes. You can use a single map, or multiple maps; put a caption on each, and consider a legend. Then discuss how well you did last week, and what contributed to any discrepancies. Refer to your map(s) in your text.

You have two choices:

  1. Turn in paper output. You do not need to use color, but your results must be clear.
  2. Turn in a computer file (HTML, Word, or Powerpoint, your choice). You can cut and paste the maps out of MICRODEM.