Lesson 2, Activity 2: Connecting
Plate Movement and Earthquakes
Student Instruction Sheet
1. Use: Map #1 = Plate Boundaries
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?
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?
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 denser that the continental one, when they collide, the denser 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?
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?
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?
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? 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://wrgis.wr.usgs.gov/docs/parks/animate/A48.gif.
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?
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?
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
Notice that the boundary between the two plates is not a straight line. Cut along the boundary between the Plate A and Plate B and then slowly move the two plates apart. Do you see 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?
4. Make a hypothesis:
Summarize what you have discovered thus far. There are areas of the plate boundaries
where the type of fault motion is primarily divergent, convergent or transform.
Hypothesize what you expect the direction of plate movement to be at these boundaries.
5. With the increase of 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 that indicate the direction of movement of the plates relative to
Africa.
Let’s see what that means:
a. One student stands up to be the reference point – Student R. 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 the two plates that are moving toward one another, creating a convergent boundary (and a subduction zone!).
- Students should notice that along California’s coast, the way in which the Pacific Plate is sliding along the North American Plate.
- Students should notice the two plates that 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?” How does the velocity of the plate movement relate to the frequency of earthquakes?
Option: You may want to take another look at the Seismic Monitor, http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-000-445, to test your prediction as to where you expect the greatest number earthquakes to occur.