How deep is the earthquake?
This activity allows students to see the relationship between earthquake depths and their locations along plate boundaries.
This final activity is best presented as a demonstration and class discussion.
Project the Mapping of Earthquakes by Depth map: http://www.teachingboxes.org/catalog.jsp?id=TBOXR-000-000-000-017.
a. Ask students to describe what they see. By now, based upon what they have learned, they will probably mention that this map portrays earthquake occurrence - earthquakes occur in a similar distribution pattern to the dots portrayed on the map.
b. Students should also notice that the dots are of different colors. Inform students that the colors indicate the depths of the epicenter of the earthquakes. Red dots represent the shallowest earthquakes. Green represents an epicenter of much greater depth; blue is the deepest. [Note: Legend to depths is to the left side of the map.]
c. Ask students to reflect on what they have learned. Where on the map would they find diverging plates, e.g. sea-floor spreading? (At the mid-oceans.) Students should note that these are areas of shallow earthquakes (red).
d. Ask students to point out areas of deep earthquakes (lots of green). Students should point to the western coast of South America as an example. These represent some of the deepest earthquakes shown on the map.
e. Ask students to recall what type of plate boundary that represents. (Convergent boundary)
f. Ask students to try to explain why this makes sense. They should recall that this is an example of a subduction zone, so that the movement of the earth is occurring at great depths as one plate slides under the other.You may want to review this with the students by using the image that they viewed earlier: http://www.teachingboxes.org/catalog.jsp?id=TBOXR-000-000-000-014.
Mapping of Earthquakes by Depth:
Illustration of subduction: