- Explain the spatial pattern of earthquakes globally to gain insight about the driving forces that cause them.
- Differentiate ways that large tectonic plates of the earth’s crust interact when they meet.
Engage: Can earthquakes occur anywhere on the planet?
Step 1: Go to the ArcGIS Online map, Cracked Plates, and explore the map.
Step 2: With the Details button underlined, click the button, Show Contents of Map (Content).
Step 3: Turn on the layer, Global Quakes of Large Magnitude 5.8, or Greater.
- Q: There are very few volcanoes or earthquakes in the middle of the Ring of Fire because this area moves as one tectonic piece, so no collisions are happening inside the tectonic plate. T/F
Explore: How many different ways can you crash a tectonic plate?
Step 4: Turn on the layer, Relative Motion at Plate Boundaries. Note that you will not see anything until you perform the next step.
Step 5: Press the button, Bookmarks.
Step 6: Select each bookmark and consider the following tectonic plate movements. South America would have a direct collision, California would have a side swipe, and the Mid-Atlantic would be torn apart.
Explain: What are these types of tectonic plates called?
Earthquakes occur where large pieces of the earth’s crust collide into (convergence), pull away from (divergence), or slide against other tectonic plates (transform).
Step 7: Turn on the layer, Plate Boundaries.
Step 8: Click the layer name, Plate Boundaries, to see its legend.
Step 9: Choose each bookmark in turn (South America, California, and the Mid-Atlantic Ridge). Analyze which ones are convergent, divergent, or transform tectonic plate boundaries.
Step 10: Turn off the layer Global Quakes of Large Magnitude 5.8 or Greater.
Elaborate: How are earthquakes distributed differently at each tectonic plate boundary type?
Step 11: Turn on the layer, South American Quakes, and pan the map to South America.
Step 12: Hover over the layer name, South American Quakes.
Step 13: Click the button, Change Style.
Step 14: Change the attribute (#1) from Show Location Only to Depth_km. The new symbology draws dots larger according to how deep earthquakes occur. Click Done to apply these changes.
- Q: Do these earthquakes occur only at the boundary between tectonic plates?
- Q: Because earthquakes happen where tectonic plates touch and only on the continent side, South America must be on top of the Pacific crust. T/F
Compare and contrast the table below with the ArcGIS maps.
|Quakes Compared to Boundary||Patterns of Depth of Quake|
|Convergent||Only one side||Gets deeper under continent|
|Divergent||Close boundary||More shallow, but random|
|Transform||Both sides of boundary||Mixed depths, but random|
Evaluate: Which type of boundary separates the Caribbean and the Gulf of Mexico?
Step 15: Turn on the layer, Caribbean Quakes.
- Q: Determine which type of tectonic plate boundary occurs here based on the table above.