There are at least three approaches for this activity:

1. Students can work in teams at the computer, following the Student Instruction Sheet.
2. Teachers can demonstrate all of these resources using a computer and projector.
3. Teachers can make colored overheads of the three maps provided.

Student Instruction Sheet (for the teacher) (Student version for copying)

1. Use: Map #1 = Plate Boundaries
http://www.teachingboxes.org/jsp/teachingboxes/plateTectonics/earthquakes/sequence/PlateBoundaries.pdf

Find South America. Notice the plate boundary along the western coast. The majority of faults along this plate boundary are of what type: (convergent)

Therefore what type of motion would you predict to find here? Plates moving away from one another, moving toward one another or sliding past one another? (moving toward one another)

So, what happens when two plates such as these collide with one another?
Open http://www.teachingboxes.org/catalog.jsp?id=TBOXR-000-000-000-014.

As the oceanic plate is more dense than the continental one, when they collide, the more dense plate “slides” under the continental plate. This is referred to as subduction.

2. Looking at Map #1 again, find the west coast of California. Notice the boundary between plates along the western coast. The majority of faults along this plate boundary are of what type: (transform)

Therefore what type of motion would you predict to find here? Plates moving away from one another, moving toward one another or sliding past one another? (sliding past one another)

Look at this photo that shows offset due to this motion:
http://www.teachingboxes.org/catalog.jsp?id=TBOXR-000-000-000-015

3. Now let’s look at mid-ocean plate boundaries. In particular, focus on the boundary that runs through the Atlantic Ocean, separating North America from Europe. The majority of faults along this plate boundary are of what type: (divergent)

Therefore what type of motion do you predict to find here? Plates moving away from one another, moving toward one another or sliding past one another? (moving away from one another) Because the plates are moving away from one another and this is occurring on the sea floor, this is referred to as sea-floor spreading.

Look at the animation found at http://128.117.226.83/catalog.jsp?id=TBOXR-000-000-000-016.
Notice that as the ocean floor spreads apart, new lithosphere is created. This is formed from magma welling up along the widening crack between two plates moving in opposite directions.

Returning to Map #1, let’s follow that boundary further south. What do you notice?
(Students should notice that there are also numerous transform faults present.) Let’s look at an enlargement of that area.

Open this resource:
SpreadingCenter2.jpg

The diagram illustrates one portion of the mid-oceanic ridge where two plates are diverging (moving away from one another). Here you can see that divergent faults (shown in blue) are interrupted by transform faults (shown in green) that are nearly perpendicular to the plate boundary. Why do you think that happens? (Encourage students to think of other “mountain ranges.” Do they run perfectly straight?)

Therefore would the motion be divergent throughout the entire mountain range? To further illustrate this, try this next activity.

Activity sheet: Plate Movement at the Mid-oceanic Ridge
SpreadingCenterGeometry.jpg

Pass out a copy of the activity sheet. Students should notice that the boundary between the two plates is not a straight line. Have students cut along the boundary between the Plate A and Plate B and then slowly move the two plates apart. They should notice that at some areas the plates are moving away from one another (divergent faults), while at other areas, parts of the plates are sliding past one another (transform faults).

4. Make a hypothesis:
Summarize with students what they have discovered thus far – that they can find areas of the plate boundaries where the type of fault motion is primarily divergent, convergent or transform. Have students hypothesize what they expect the direction of plate movement to be at these boundaries.

5. With the increase in technology, geologists have been able to determine the direction and velocity of plate movement.

Take a look at Map #2:
PlateBoundaryVelocityDirection.pdf
Here you will notice that most of the plates have been named and arrows have been added to indicate the direction of movement of the plates relative to Africa.

Let’s see what that means:
a. Have one student stand up to be the reference point – Student R. Let four other students stand with their backs to Student R. While Student R. stands still, the other students should each take 4-5 steps forward. This illustrates that the four students are all moving in different directions relative to Student R.

b. Similarly, in this map, the direction of the plate movements is indicated relative to a “stationary” Africa. Notice how South America is moving away from Africa.

c. Find the same areas that you have just investigated. Look at the direction of the arrows. Were your predictions correct?

- Students should notice that South American and Nazcan plates are moving toward one another, creating a convergent boundary (and a subduction zone!).
- Students should notice that along California’s coast, the arrows indicate that the Pacific Plate is sliding northwestward along the North American Plate.
- Students should notice that the Pacific and Nazca plates are moving away from one another, creating a diverging boundary (sea-floor spreading!).

6. Now let’s look at Map #3:
PlateBoundariesVelocities.pdf

In this map, the arrows still indicate the direction of movement, but they now appear to be of differing lengths. The length of the arrow is indicative of the velocity – the longer the arrow, the greater the velocity.

In what part of the world do you find the “longest arrows?” (Islands of the South Pacific)

How does the velocity of the plate movement relate to the frequency of earthquakes? (The greater the velocity, the more frequent the earthquakes.)

Option: You may want to have students take another look at the Seismic Monitor, http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-000-445, to test their prediction as to where they expect the greatest number earthquakes to occur.

Map #1 = Plate Boundaries: http://www.teachingboxes.org/jsp/teachingboxes/plateTectonics/earthquakes/sequence/PlateBoundaries.pdf

Image of subduction zone:
http://www.teachingboxes.org/catalog.jsp?id=TBOXR-000-000-000-014

Image of earthquake offsets:
http://www.teachingboxes.org/catalog.jsp?id=TBOXR-000-000-000-015

Animation of sea-floor spreading:
http://wrgis.wr.usgs.gov/docs/parks/animate/A48.gif

Diagram of mid-oceanic ridge: http://www.teachingboxes.org/jsp/teachingboxes/plateTectonics/earthquakes/sequence/SpreadingCenter2.jpg

Map #2: http://www.teachingboxes.org/jsp/teachingboxes/plateTectonics/earthquakes/sequence/PlateBoundaryVelocityDirection.pdf

Map #3:
http://www.teachingboxes.org/jsp/teachingboxes/plateTectonics/earthquakes/sequence/PlateBoundariesVelocities.pdf

Plate Movement at Mid-Ocean Ridge activity: http://www.teachingboxes.org/jsp/teachingboxes/plateTectonics/earthquakes/sequence/SpreadingCenterGeometry.jpg

Prepare Student Instruction Sheet and make copies.
Make copies of activity sheet: SpreadingCenterGeometry.jpg
Prepare handout for assessment:
http://www.teachingboxes.org/catalog.jsp?id=SERC-STARTINGPOINT-000-000-000-331