Part 4—Investigate Earthquakes and their Distribution

Step 1 – Launch My World and Set up the Map

1. Launch My World.
2. Make sure you are in Construct mode. (Click the "Construct" tab at top of screen to change modes).
3. Select Geology from the Data Library pull-down menu.
4. Click and drag the following layers to your Layer List:
   
   • *Continents
   • *Plate Boundary Types
   • Earthquakes - Medium 4.0-5.9 (2001-2003)
   
   Optional:
   • Earthquakes - Big 6.0-9 (1994-2003)
   • Earthquakes - Small 2.0-3.9 (2001-2003)
5. If you are continuing from Part 2 the first two layers will already be on your map.
6. Switch to Visualize mode by clicking the Visualize tab.

Step 2 – Explore the Depths of Earthquakes

1. Open the table of the layer for the Earthquakes Medium... layer to investigate its contents. Sort the "Depth and Magnitude" fields ascending and descending. Note the ranges of values for both of these fields.
Show me how to use the table
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1. You can open an activated layer's table choosing Layer > Show Layer Table or by clicking the Show Table of Selected Layer button above the map.


2. Sort a field by clicking on the field name. Each click will sort the field, ascending , descending , and then back to unsorted.
3. In the Layer List, classify the Earthquake layer by choosing "Depth" from the pull-down menu.
   
Legend Tip: You can toggle a layer's legend on and off by selecting the "Hide/Show Color Legend" button.


2. Close the Table of the Layer.
3. Use the map to explore the visual patterns in Earthquake locations? Provide a possible reason why Earthquakes occur in these locations.
4. Create a series of selections of shallow (0-199) and medium (200-399) and deep (400 and greater) earthquakes using the 'select by value' in Analyze mode.
Highlight Mode Tip: After making a selection in Analyze mode, try different Highlight Modes to see different ways to display your selection .
5. Select the earthquakes by magnitude.
• Select items from "earthquakes medium..." whose "depth is greater than "400." Provide a result name that will describe the selection.
• Return to Analyze mode and create the additional selections from "earthquakes medium..." Provide result names that will describe the selection.
6. Consider the following questions:
• Switch between the different selections and make observations of where earthquakes of different depths occur.
Show answer
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The earthquakes tend to occur around the plate boundaries. This probably happens because most of the plate activity occurs around the boundaries.


• Where do the deepest (400km and greater) earthquakes occur?
Show answer
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The deepest earthquakes occur near the plate boundaries that are around eastern Asia. There are also some in the Pacific Ocean and in South America.


• Why do you think earthquakes are deepest at these locations?
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These locations are where the most active plate boundaries are, and the subduction zone is the deepest.


• Where do the shallowest (0-199km) Earthquakes occur?
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The shallowest earthquakes occur all around the globe, but are mainly inland and in close proximity to the plate boundaries.


• Why do you think earthquakes are shallowest at these locations?
  
  Show me a hint
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  Turn on the Plate Boundary Types layer and observe the relationship between plate boundaries and earthquakes of varying depths. Change the legend of the Plate Boundary Types layer to "Margin Type."
  Show me the answer
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  These locations have the shallowest earthquakes because they are closest to the plate boundaries or are in plate interiors. Also, many of the shallow earthquakes lie along the divergent boundaries as well. Divergent boundaries are where two plates are moving apart from one another.

Step 3 – Observe the Relationship between Earthquake Patterns at Different Types of Plate Boundaries

Now that you have investigated seafloor age and volcano activity, you will look for one more relationship in support of the theory of plate tectonics. To do this, turn on the Plate Boundaries layer and observe the relationship between plate boundary types and earthquake patterns.

1. Consider the following questions while looking at the map:
   • What is the pattern of earthquake depths at a divergent boundary?
   Show answer
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   The earthquakes at the divergent boundaries tend to be mild and do not go very deep.
   
   
   • What is the pattern of earthquake depths at a convergent boundary?
   Show answer
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   Earthquakes around the convergent boundaries range from shallow to deep depending on the location of the subducting plate in relationship to the overlying plate.
   
   
   • What differences do you notice between these two boundary types?
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   The convergent boundaries can be between ocean and land, land and land, or ocean and ocean. Divergent plate boundaries tend to be on the ocean floor, with few exceptions on land.
   
   
   • Is the pattern of earthquakes similar on both sides of the plate boundary? Explain the pattern you observe.
   Show answer
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   Because they are underwater, the earthquakes along the divergent boundaries are similar on both sides. For the convergent boundaries, the earthquakes tend to occur in the overlying plate.
   • Summary question: For each boundary type, list evidence you've discovered that describes plate movement.