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Plate Tectonics
TEACHING TRANSPARENCY
54
Locations of Earthquakes in
South America, 2002–2003
75ºW
60ºW
45ºW
30ºW
0º
SOUTH
AMERICA
15ºS
30ºS
Earthquake Depth (km)
PACIFIC
OCEAN
0
25
ATLANTIC
OCEAN
75
150
45ºS
300
600
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Locations of Earthquakes in South America, 2002-2003
This map shows the locations and depths of earthquakes that registered magnitudes greater than 5 and happened in South America in 2002 and 2003. Use the
map to answer the questions below.
1. Using the Key How many earthquakes happened at a depth greater than 300 km?
2. Analyzing Data Deep earthquakes are earthquakes that happen at a depth
greater than 300 km. Which earthquakes happen more frequently: deep
earthquakes or shallow earthquakes?
3. Making Comparisons How does the earthquake activity on the eastern edge of
South America differ from the earthquake activity on the western edge?
4. Inferring Relationships The locations of earthquakes and plate boundaries are
related. Where would you expect to find a major plate boundary?
5. Identifying Trends In what part of South America do most deep earthquakes
happen? What relationships do you see between the locations of shallow and
deep earthquakes in South America?
6. Analyzing Relationships Most deep earthquakes happen when subducting
plates move deeply into the mantle. What type of plate boundary is indicated
by the earthquake activity in South America? Explain your answer.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Earth Science
Plate Tectonics
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ANSWER KEY
2. shallow earthquakes
3. In the time period shown, no earth-
2. The denser oceanic crust is subducted
under the less dense continental crust,
where it releases water, causing the
mantle above to melt. Some magma
may rise through the continental crust
and form volcanic mountains.
3. The plates are sliding horizontally past
each other at a transform boundary.
4. The buildup of tension between sticking plates would produce the most
severe earthquake along a transform
boundary.
5. The top diagram shows crust being
created at a mid-ocean rift; the center
diagram shows crust being “ destroyed”
at a subduction zone.
quakes with magnitude greater than
5.0 occurred on the east coast, but
many occurred on the west coast.
4. along the western coast of South
America
5. Most deep earthquakes happen toward
the center of the continent. As you
move east from the west coast, the
earthquakes tend to get deeper.
6. The plate boundary on the west coast
of South America is probably a convergent boundary (subduction zone).
The subducting plate is moving eastward under the continent. As the subducting plate moves down under the
continent, the earthquakes get deeper
because the plate boundary is deeper.
52 Ridge Push and Slab Pull
1. The older crust is denser because
it’s shown sinking beneath the newly
formed crust.
2. Ridge push moves crust away from the
mid-ocean ridge.
3. the plate to the left, which is subducting
4. its greater density
55 Isostatic Adjustment
1. Isostasy is the balance between the
forces of gravity and buoyancy that
allows Earth’s crust to be stable.
2. weathering or erosion of surface rock
3. The lithosphere rises to compensate
and regain the balance.
4. The growth of an ice sheet would cause
the lithosphere beneath the ice to sink,
and the ocean floor to rise. The retreat
of a glacier would cause the land
underneath the melting glacier to rise,
and the ocean floor to sink.
53 The Supercontinent Cycle
1. Siberia and North America were
2.
3.
4.
5.
located on the equator; North America
and Europe were differently shaped
islands; and Africa, South America,
and Antarctica comprised one continent.
about 20 million years
Answers may vary. Sample answer:
The development of a single landmass
would have vastly reduced the amount
of coastal areas, which generally support a great diversity of marine species, and instead formed an enormous
open ocean with relatively little coastline.
You might expect them to continue to
separate, moving across the Pacific
and perhaps colliding and forming
a single landmass once again many
years from now.
somewhere in what is now the Pacific
Ocean, based on the current rate of
tectonic plate movement
56 Types of Stress
1. Stress is the force acting on the
2.
3.
4.
5.
lithospheric rock, such as squeezing,
stretching, and twisting.
its volume is reduced and it is pushed
higher up or deeper down into the
crust
Tension stretches and pulls rock apart,
and the rock becomes thinner.
Shear stress acts on rock by pulling in
opposite directions, tension stretches
and pulls, and compression squeezes
and shortens.
Shear stress, because of the horizontal
movement of tectonic plates past each
other
57 Folds
54 Locations of Earthquakes in
South America, 2002-2003
1. the plane that slices a symmetrical
1. about 11
fold into two symmetrical halves
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Earth Science
14
Answer Key