Name:_________________________
Earthquakes and Plate Boundaries
Date:___________ Period:_____
Introduction:
Why do earthquakes occur where they do? What causes earthquakes? Are earthquakes
related to any earth structures? The earth’s outer shell of rock is believed to be made up of a
number of rigid plates, called Lithospheric plates, which are from 80 km to 160 km thick.
The plates are made up of the two upper rock zones of the earth, the crust and the upper
portion of the mantle. Some plates include only oceanic crust. Other plates include both
oceanic and the lighter continental crust. These plates ride on a zone in the mantle where
the rock is almost melted and therefore not rigid. An example to help you picture this would
be a black of wood floating in a bowl of honey.
In this activity you will find out that different patterns of earthquakes and topography are
related to different kinds of plate boundaries.
Instructions:
Go to the following website and use the images and information to answer the following 13
questions.
http://www.classzone.com/books/earth_science/terc/content/investigations/es1001/es1001page01.cfm
1. Predict where most earthquakes occur.
2. What kind of plate boundary lies along the edge of California?
3. Describe how the pattern of earthquake locations compares to the location of plate
boundaries.
4. According to the map, what type of plate boundary seems to be associated with a
greater number of earthquakes?
5. Hypothesize as to how some earthquakes can occur in areas that are not along plate
boundaries.
6. Which depth range has
a. the most earthquakes?
b. the fewest earthquakes?
7. At what type of plate boundary do you find most deep-focus earthquakes?
8. Explain why deep-focus earthquakes occur at this type of plate boundary but not at
others.
9. Which magnitude range has the
a. greatest number of earthquakes?
b. fewest number of earthquakes?
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10. Which type of plate boundary experiences the most earthquakes with large
magnitudes?
a. Hypothesize about why that type of boundary experiences larger earthquakes
than the others.
11. Give three examples of damage that can occur as a result of earthquakes.
a.
b.
c.
12. Looking at the picture from Anchorage, AK, what secondary natural disaster can be
caused by certain earthquakes?
13. Which cities are susceptible to earthquake activity?
a. Describe the factors you considered in order to arrive at your answer.
Ring of Fire
The Ring of Fire describes a zone of frequent earthquakes and volcanic eruptions that
encircle the Pacific Ocean. The Ring of Fire exists along the edges of tectonic plates, often
at the edges of continents. It stretches from the southern tip of South America to Alaska,
then across the Pacific Ocean to Japan, Indonesia and New Zealand. Volcanoes of the
Cascade Range are part of the Ring of Fire. Each Cascade volcano represents one link of
this long chain of volcanoes.
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1. Examine the map of Earth’s tectonic plates above. Name some of the larger plates
that touch the Pacific Plate.
2. Look for patterns in the general distribution of earthquakes and volcanoes on this map.
Describe them.
3. Name the plate that is surrounded on three sides by a ring of earthquakes and
volcanoes. Why do you suppose they call this the “Ring of Fire”.
4. Label it on your map.
5. Place a circle around the general area of the Cascade volcanoes.
6. Locate three other areas on the earth’s surface which would most likely have
subduction zones.
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Plate Tectonics – Cascade Range
The Pacific Ocean may look calm on its surface, but the floor beneath it moves eastward
continuously off the coast of the Pacific Northwest at a rate of approximately 5 centimeters (2
inches) each year. In the Pacific Northwest, the Pacific and North American plates are
separated by a small tectonic plate called the Juan de Fuca Plate. As the Juan de Fuca Plate
inches eastward it pulls away from the Pacific Plate, opening a gap that enables magma to
rise and construct submarine volcanoes in the Juan de Fuca Ridge. Scientists refer to this
pulling apart as a divergent plate boundary or spreading ridge. Further east, the Juan de
Fuca and North American plates move toward each other at a convergent plate boundary.
Dense rock of the Juan de Fuca Plate sinks beneath the North American Plain in a process
called subduction. We call this region the Cascadia Subduction Zone. The north and south
edges of the Juan de Fuca plate slide past neighboring plates at transform plate boundaries.
On the Plate Tectonics-Cascade Range map, the shaded triangles indicate the location of
Cascade volcanoes. Triangles on the line show the location of the Cascadia Subduction
Zone.
Instructions:
1. On the Plate Tectonics-Cascade Range map, label the divergent, convergent and
transform plate boundaries on the map where you see numbered blanks 1-4. You will
use one label twice.
2. Does the eastern boundary of the Juan de Fuca Plate lie parallel to the Cascade
Range?
3. Does the line of volcanoes extend north and south of the converging plates? Make a
hypothesis that explains your answer.
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Using Earthquakes to Find the Subduction Zone – Questions
1. Explain why earthquakes can occur in abundance at this plate boundary.
2. Make a prediction about the location of earthquakes on the graph. Predict the pattern of
earthquakes at this convergent plate boundary. Trace the predicted pattern lightly in pencil on
the graph.
3. Plot the location of earthquakes on the graph using the depth and location data provided.
4. Examine the pattern of earthquakes on the diagram. Does the pattern of platted
earthquakes confirm your prediction? Explain how the depth of earthquakes varies across the
region shown on the graph.
5. Write a hypothesis about why the pattern of earthquakes shows curvature.
6. Find the depth at which the earthquakes cease. Write your answer below.
7. In the previous section, you discovered that Cascade volcanoes are positioned parallel to
the plate boundary between the Juan de Fuca and North American plates. Use this
information to form a hypothesis that explains the location of the volcanoes.
8. Use the information in the text to calculate how long it will take for the entire Juan de Fuca
Plate to subduct beneath North America.
10. Describe what a subduction zone is, as you would to a 3 rd grader.
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