Download earthquakes our restless planet

EARTHQUAKES
OUR RESTLESS PLANET
1 videocassette
22 minutes
Copyright MCMXCV
Rainbow Educational Media
4540 Preslyn Drive
Raleigh, NC 27616-3177
Distributed by:
United Learning
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Evanston, IL. 60201
800-323-9084
www.unitedlearning.com
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PRINCIPAL CREDITS
Producer, Writer and Director:
Peter Matulavich
Consultants:
Jim Mori, Ph.D. Scientist
in Charge United States
Geological Survey
Michael Worosz, M.A.
Curriculum Consultant
Associate Producer:
Videography & Animation:
Production Manager: Special
Thanks to:
Diann Fried Peter
Matulavich Roxanne
Hall
United States Geological
Survey
National
Geophysical Data
Center
KTVUTV
Video and Teacher's Guide produced for
Rainbow Educational Media
by Peter Matulavich Productions
San Dimas, California
TABLE OF CONTENTS
Introduction
2
Objectives
3
Summary
4
Review Questions
7
Discussion Questions
9
Activities
12
Glossary
14
Bibliography
16
Script
20
INTRODUCTION
This video is designed to introduce students to the
subject of earthquakes, their causes and their effects.
Few natural forces create such destruction and instill
such awe as earthquakes, yet it has been only in recent
years that scientists have determined the primary cause
of earthquakes: the grinding of the tectonic plates
which compose our planet's shell.
Students will learn through exciting, full-motion
animation that the earth's plates move as a result of
movement in the material that makes up the earth's
mantle. The mantle movement isn't slow and gradual,
but rather occurs in spurts when sufficient stress
builds up along faults in the earth's crust, and one side
of the fault lurches past the other. The energy that is
released is in the form of seismic waves which move
outward in all directions, not unlike the waves that
occur when a stone is tossed into a pond. When
seismic waves reach the earth's surface they can cause
considerable destruction and loss of life.
In the video's conclusion, students will learn that
scientists continually study and monitor earthquakes in
the hope that they might someday be able to forecast
earthquakes, thereby reducing potential destruction and
loss of life.
2
OBJECTIVES
After viewing this video, students should know:
•
the names of the earth's interior layers
•
the concepts of continental drift and plate
tectonics
•
the cause of plate movement
• the three types of plate boundaries
•
the location and importance of the midocean ridge
•
the locations and importance of subduction
zones
•
the cause of most earthquakes
•
the devastating power of some
earthquakes
•
areas where earthquakes are most likely to
occur
•
the location of the San Andreas fault
•
types of monitoring equipment used by
scientists to study earthquakes
•
how earthquakes are measured
3
SUMMARY
The video opens with dramatic scenes of the Loma Prieta
earthquake of 1989. Students learn that while the quake
lasted only 15 seconds, 67 people were killed and damage
was widespread. The narrator poses these questions:
What causes earthquakes? Why do earthquakes occur in
some places but not in others? Will scientists ever be able
to forecast earthquakes?
Next, we see students examining a large globe. As useful
as globes are they are unable to tell us what's inside our
planet.
Full motion animation then reveals the various layers of
the earth's outer shell, the lithosphere, which consists of
the crust and the rigid, outer portion of the earth's mantle.
Students leam that the earth's shell is cracked into more
than a dozen pieces called plates, and that each plate carries
a continent, or an ocean basin, or sometimes both. The
positions of these plates are only temporary. They are
moving at an average rate of one to four inches a year in a
variety of directions, carrying continents and ocean basins
with them.
Animation reveals what the continents looked like millions
of years ago and how they slowly reached their presentday positions. Animation also shows what the world will
look like millions of years in the future as the continents
continue their slow dance around the globe.
The video then discusses what causes the plates to move:
the circulating movement of magma within the earth's
mantle. Students learn that in some places, plates covering
ocean basins are moving apart and, as they do, magma
rises from the mantle to fill the gap.
4
This process is referred to as sea-floor spreading and
the area where magma rises is known as a mid-ocean
ridge. A mid-ocean ridge circles the globe, generating
new plate material along its length. The video
discusses how plate movement along the mid-ocean
ridge is responsible for numerous underwater
earthquakes.
Earthquakes also occur near other types of plate
borders: subduction zones and transform faults.
Subduction zones are areas where one plate dives, or
subducts, beneath another. Transform faults are areas
where plates slide past each other.
We learn that the grinding of plates has been going on
for so long that the earth's crust is filled with cracks
referred to as faults, and it is in these faults that
earthquakes originate. Faults are locked in place most
of the time, but when enough stress builds up, the
fault will suddenly slip, one side sliding past the
other, releasing energy in the form of seismic waves.
The waves generated in earthquakes are similar to the
waves created when a stone is tossed into a pond. If
the disturbance is big enough, seismic waves reach
the earth's surface where they can cause considerable
destruction. We learn that the place where a fault
slips is called the earthquake's focus and the point of
the earth's surface directly above the focus is called
the earthquake's epicenter.
Next, the video discusses the work being conducted
by earthquake scientists. We follow a scientist into
the mountains where he buries a seismometer (a
monitoring device) which will be part of an
earthquake monitoring network. Next, the video
segues to a control room where powerful computers
receive data from hundreds of buried seismometers.
The computers help scientists determine the location
and size of an earthquake.
5
Students will then see that different types of seismic
waves are associated with earthquakes. Animation
shows the characteristics of P (primary) and S
(secondary) waves.
The video concludes with the discussion that millions
of people live in seismically-active areas and that's
why scientists hope that they will one day be able to
forewarn people of impending earthquakes.
6
REVIEW QUESTIONS
1.
What are the earth's interior layers?
The layers are the inner core, the outer core, the
mantle and the lithosphere or shell.
2.
What composes the lithosphere?
The lithosphere is composed of the crust and
upper portion of the mantle.
3.
The lithosphere is broken into more than
a dozen pieces. What are these pieces
called?
They are called tectonic plates.
4.
What causes the earth's tectonic plates
to move?
The movement of plates is caused by the
movement of magma within the mantle.
5.
What is the difference between magma
and lava?
Lava is the name for magma after it erupts from
volcanoes.
6.
What is the mid-ocean ridge?
It is an area where two plates move apart
allowing magma to rise and fill the resultant gap.
7.
What are subduction zones?
Subduction zones are areas where one plate
dives beneath another, becoming consumed
back into the earth's mantle.
7
8.
What causes earthquakes?
Earthquakes are caused by sudden movements
along faults.
9.
Seismic waves can be compared to what
other types of waves?
They can be compared to the waves created
when a stone is tossed into a pond.
10. What is the earthquake's focus?
The place where a fault slips is referred to as the
earthquake's focus.
11. What is the earthquake's epicenter?
It is the point on the earth's surface directly
above the focus.
12. What is a seismometer?
It is a device used to measure the amount and
degree of shaking during an earthquake.
13. What is the Richter scale?
It is a scale used to gauge the magnitude of an
earthquake.
14. Can scientists forecast earthquakes?
No, but they hope they will be able to do so in
the future.
8
DISCUSSION QUESTIONS
These questions are designed to
encourage classroom discussion
1.
While not discussed in the video, ancient
peoples attributed earthquakes to a variety
of unscientific causes. For example,
Hindu mythology describes an earth
supported by eight mighty elephants. An
earthquake would result when one of the
elephants bowed its head.
Explain the occurrence of earthquakes as they
might've been explained by ancient peoples.
Answers include earthquakes being attributed to
angry gods venting their anger; the jostling caused
by giant animals and beasts; and various
supernatural explanations.
2.
The video discusses why earthquakes
occur in some areas but not in others.
What is the likelihood of an earthquake
occurring in the area in which you live?
Answers, of course, vary with each locality.
Many earthquakes occur in California, Alaska, and
other Pacific states. One of the country's largest
earthquakes occurred in Missouri over a century
ago, and no area is immune to earthquakes.
9
3.
The video depicts the tremendous
devastation, loss of life and injuries
caused by earthquakes.
What earthquake safety precautions can people
take to minimize injuries, damage, and death?
While not discussed in the video, there are
numerous safety precautions and many rely
greatly on common sense. A few include:
- staying calm, not panicking.
- seeking protection under heavy tables, beds,
door jams
-securing heavy objects, i.e. bookcases,
mirrors, water heaters
- knowing where and how to shut off the gas in
the event of a gas leak
- maintaining emergency food and water
- avoiding damaged structures
4.
The video discusses plate tectonics as
the mechanism behind the occurrence of
earthquakes.
What other natural phenomena can be
explained by plate tectonics?
Continental drift, volcanism, and mountain
building can all be explained by plate tectonics.
5.
Earthquakes occur throughout the world
with frightening regularity.
Ask students to recall and discuss earthquakes
-with which they are familiar.
Answers might include: 1994 Northridge,
California; 1989 Loma Prieta, California ; 1976
Tangshan, China; 1971 San Fernando,
California; 1964 Anchorage, Alaska; 1948
Fukui, Japan; 1906 San Francisco.
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6.
Many people, including scientists,
believe that animals can sense an
impending earthquake.
What could explain this ?
While no one can say with certainty how, or
even if, animals can sense an impending
earthquake, it is common knowledge that many
animals have keener senses than humans and
some have abilities which we do not. For
example, catfish are believed to be sensitive to
vibrations . Some people believe dogs, horses,
and snakes to be similarly sensitive.
7.
Many of the casualties and much of the
destruction experienced in some
earthquakes are not the results of
earthquakes themselves, but occur
afterward.
What are some other hazards directly associated
with earthquakes?
Fires from broken gas lines, landslides from
weakened ground, and floods from broken
dams, have all contributed to earthquake
destruction and casualties.
8.
The video discusses that someday, scientists
may be able to forecast the occurrence of
earthquakes.
What benefit would a 24-hour earthquake warning
provide a city?
While some lives might be saved, others might
be lost in the panic to escape the city.
11
ACTIVITIES
These activities are designed to encourage
students to learn more about some of the
things covered in the video.
1.
The video discusses how stress builds
along a fault before it slips with a
sudden jerk.
Activity: This can be simulated by having
students press their hands together and then try
to slide one past the other. Often, their hands
will slip with a sudden jerk. Students can also
bend sticks until they suddenly snap.
2.
P and S waves were discussed in the
video as the first two types of seismic
waves to reach the earth's surface.
Activity: Students can mimic the motion of P
waves by stretching a slinky and then allowing it
to retract. Coils of the slinky will alternately
stretch and contract, much like the motion of P
waves.
Activity: Students can mimic the motion of S
waves by tying one end of a long rope to an
object, and then jerking the other end with a
whip-like motion to create a wave that travels the
length of the rope.
3.
The video discusses that an earthquake's
destructive capability is greater near the
epicenter.
12
Activity: Have students set up about a dozen
dominoes on top of a large cardboard box. Next,
have a student thump one end of the box,
observing which dominoes are the first to fall.
Generally, the dominoes closest to the thumping
will fall first.
4.
The video discusses several devastating
earthquakes such as the Loma Prieta
earthquake of 1989.
Activity: Have students research and report on a
devastating earthquake.
5.
The video discusses how earthquakes
occur along plate boundaries.
Activity: Have students draw a map of the
world, marking plate boundaries and locating
recent earthquakes.
13
GLOSSARY
continental drift: theory that continents can drift
convergent boundary: boundary where two
plates come together
crust: thin outermost layer of the earth
destructive: able to cause great damage
divergent boundary: boundary where two plates
move apart
epicenter: point on the earth's surface that lies
directly above an earthquake's focus
fault: crack in a rock, one or both sides of which
have moved in relationship to the other
focus: point within the earth where movement along
a fault creates an earthquake
inner core: solid innermost layer of the earth
lava: molten rock that erupts from the earth
lithosphere: outer layer of the earth composed of the
crust and outermost portion of the mantle
magma: name for lava before it reaches the earth's
surface
magnitude: size of an earthquake measured by the
amount of energy released
mantle: mostly molten layer of the earth located
below the crust
14
mid-ocean ridge: undersea mountainous ridge and
divergent plate boundary that circles the earth
outer core: molten layer of the earth located below
the mantle
P wave: first seismic wave to reach the earth's
surface
Richter scale: scale used to measure the magnitude
of earthquakes
San Andreas fault: 500-mile-long transform fault
that divides California
seismic wave: shock wave caused by an
earthquake
seismogram: record made by a seismometer
seismometer: instrument used to record the
movement of the ground during an earthquake
shell: informal name for the lithosphere
subduction zone: convergent boundary where one
tectonic plate descends beneath another
S wave: second seismic wave to reach the earth's
surface
tectonic plates: rigid moveable sections of the
lithosphere
transform boundary: boundary where two plates
slide past each other
15
BIBLIOGRAPHY
Ballard, Robert D. Exploring Our Living Planet.
National Geographic Society, Washington, D.C.,
1983.
Bernstein, Leonard and Wong, Harry K. Earth Science,
2nd ed. Globe Book Co., New Jersey, 1979.
Calder, Nigel. The Restless Earth. Viking Press, 1972.
Cattermole, Peter and Moore, Patrick. The Story of the
Earth. Cambridge Univ. Press, 1985.
Clark, John. Earthquakes to Volcanoes. Gloucester
Press, New York, 1992.
Editors of Time-Life Books. Volcano. Time-Life Books,
Alexandria, VA, 1982.
Erickson, Jon. Rock Formations and Unusual Geologic
Structures. Facts on File, Inc., New York.
Erickson, Jon. Volcanoes and Earthquakes. Tab Books,
Inc., 1988.
Frances, Peter and Jones, Pat. Images of Earth.
Prentice Hall, Inc., New Jersey, 1984.
Harris, Stephen L. Fire and Ice. Pacific Search Press,
1980.
16
Harris, Stephen L. Agent of Chaos. Mountain Press
Publishing Co., Missoula, Montana, 1990.
Kaye, Glen. Hawaii Volcanoes. KC Publications, 1976.
Lutgens, Frederick and Tarbuck, Edward. Essentials of
Geology, 4th ed. Macmillan Co., New York,
1989.
Marvin, Ursula. Continental Drift. Smithsonian Institution
Press, 1973.
Mather, Kirtley F. The Earth Beneath Us. Random
House, New York, 1964.
Miller, Russell. Continents in Collision. Time-LifeBooks,
Alexandria, VA., 1983.
Redfern, Ron. The Making of a Continent. Times Books,
New York, 1986.
Simpson, Brian. Minerals and Rocks. Galahad Books,
New York, 1974.
VanCleave, Janice. Earthquakes, Spectacular Science
Projects. John Wiley & Sons, New York, 1993.
VanCleave, Janice. Volcanoes, Spectacular Science
Projects. John Wiley & Sons, New York, 1994.
Van Rose, Susanna and Marcer, Ian F. Volcanoes. British
Museum, 1991.
Van Rose, Susanna. Volcano & Earthquake. Alfred A.
Knopf, 1992.
Walker, Bryce. Earthquake. Time-Life Books,
Alexandria, VA., 1982.
Weiner, Jonathan. Planet Earth. Bantam Books, New
York, 1986.
17
Wright, Thomas and Takahashi, Taeko and Griegs, J.D.
Hawaii Volcano Watch. Univ. of Hawaii Press,
1992.
Zike, Dinah. The Earth Science Book. John Wiley &
Sons, Inc. 1993.
18
SCRIPT
In 1989, a major earthquake strikes Northern
California. While the quake lasts only 15 seconds, 67
people are killed and damage is widespread.
Each year, thousands of earthquakes occur
throughout the world. While most are minor, a few
cause great damage and loss of life.
What causes the earth to rumble and shake? Why do
some areas of the world experience earthquakes and
others do not? Will scientists ever be able to forecast
earthquakes?
We're all familiar with a globe. It shows what our
planet looks like from the outside. It shows the great
land masses, called continents, and the bodies of
water, called oceans. As useful as globes are, they
are unable to show you one very important part of our
planet, the inside.
The earth's interior consists of several different
layers: the inner core which is believed to be solid
iron and which is very hot; the outer core which is
believed to consist of rocky material so hot and under
such great pressure that it is in a liquid state; the
mantle which is not so hot as the outer core and not so
liquid.
The mantle's outermost portion is solid.
This is the solid outer portion of the mantle. Above
this, the outermost layer of the earth, the crust.
Together, the crust and the solid outer portion of the
mantle form the earth's outer shell. They are referred
to as the lithosphere.
20
It's not always easy to see the earth's crust. It is
covered by vegetation and oceans; but if you could
drain the earth's oceans and strip away our planet's
vegetation, the earth might look something like this.
Now we can see the earth's hard outer shell, and if
you look closely, you can also see where the shell is
cracked. The red glowing lines mark the places
where the earth's shell is cracked into small and large
pieces called tectonic plates.
Each plate carries a continent, or an ocean basin, or
sometimes both.
The plates are moving at one to two inches a year in a
variety of directions, carrying continents and ocean
basins with them.
Millions of years ago, the earth looked something like
this, every continent in a different position. They
were so close together, they formed a single, super
continent, called Pangaea; but even then, the plates
were moving, a few inches a year, and kept moving,
until they reached their present-day positions.
The theory that continents move is called continental
drift.
When you look at a globe today, you are looking at
only a moment in time, because the continents are still
moving, inches a year, too slow to see, as they move
farther and farther apart. Then the continents will
stop moving apart. They will change directions,
coming together once again. Millions of years from
now, scientists expect the world to look entirely
different; every continent in a new position, carried
there by the moving plates.
21
While we can't see this movement occurring, we can
see the effects.
Earthquakes are just one of several dramatic effects of
plate movement.
Here's why the plates are moving. Scientists believe
material in the mantle is circulating much as it is doing
here. The movement may be caused by heat within
the mantle.
You can get an idea of how heat can cause a
circulating movement, by watching rice as it boils.
What you see happening within this beaker is similar
to what's happening within the earth's mantle. As
mantle material moves, perhaps only inches a year, it
causes the plates above it to move as well.
In some places, plates are moving in opposite
directions. They are moving apart. The area where
two plates are moving apart is called a divergent
boundary. Most divergent boundaries are located
below oceans.
This is a cross-section of a divergent boundary,
located below the Atlantic Ocean. Scientists have
discovered that as the plates move apart, hot liquid
rock, called magma, rises from the earth's mantle.
The magma rises because it is lighter than the
surrounding material.
Magma is the name we give lava before it erupts from
volcanoes, as it is doing here; and just as this lava is
doing, magma hardens into rock when it cools.
As the magma rises and cools, it adds new crust to
old, spreading the ocean floor. This area of rising
magma is known as a mid-ocean ridge.
22
This shows where magma is surfacing between plate
boundaries, creating a mid-ocean ridge that circles the
earth.
The ocean floor spreads in one direction on one side
of the ridge, and in the opposite direction on the
other.
The mid-ocean ridge is where plate material is
created.
This is where plate material is destroyed; an area
where two plates are colliding, a convergent
boundary.
This is a cross-section of a convergent boundary. In
this example, the plate on the right is carrying an
ocean basin and is moving in this direction. The plate
on the left is carrying a continent and is moving in the
opposite direction. The plate carrying the ocean basin
is heavier and is diving beneath the plate carrying the
continent. The leading edge of the diving plate is
consumed back into the earth's mantle.
When one plate dives beneath another, it is called
subduction, and the area where it occurs is called a
subduction zone.
Subduction may resemble what is happening on this
lava lake, as sections of hardened crust dive beneath
other sections.
The highlighted areas on this globe mark convergent
boundaries. Subduction is occurring at most of them.
These are the areas where plate material is destroyed.
Here again are divergent boundaries, where plate
material is being created. Again, most of them are
beneath the oceans, creating a mid-ocean ridge that
circles the planet.
23
The grinding of plates has been going on for so long
that most of the earth's crust is filled with cracks, not
unlike the way this rock is filled with cracks.
Scientists refer to a crack in the earth's crust as a
fault, and it is in these faults that earthquakes
originate.
One side of the fault tries to move in one direction.
The other side of the fault tries to move in a different
direction, but the two sides are locked in place. They
can't move until enough stress builds up to move
them.
If you were to bend a stick slowly, you would find
that it won't break until sufficient stress builds up.
That's what happens deep underground, the fault will
remain locked until enough stress builds up, and then
it will suddenly release, one side of the fault sliding
past the other with a tremendous burst of energy.
The energy that is released is in the form of seismic
waves which radiate, or move outward.
If the disturbance is big enough, the waves will
eventually reach the surface, where they can cause
considerable movement referred to as an earthquake.
The place where a fault slips is called the earthquake's
focus.
The point on the earth's surface directly above the
focus is called the earthquake's epicenter.
What's interesting about earthquakes is how most of
them coincide with plate boundaries.
24
These dots mark the locations of recent worldwide
earthquakes. These lines mark plate boundaries. You
can easily see how most earthquakes occur along plate
boundaries.
They occur near divergent boundaries, convergent
boundaries, and they occur near the third type of
boundary, a transform boundary. This is where two
plates slide past each other.
The world's most famous transform boundary is located
in California. It splits the state into two sections.
Here, the plate on the left is being driven in this
direction. The plate on the right is being driven in the
opposite direction.
The two plates will remain locked until sufficient
tension builds up between them, and then they will
release in a sudden jerk, causing an earthquake.
The amount of movement might only be a few inches,
but could be several feet.
The giant fault that is created by this plate movement is
called the San Andreas fault.
In some places the fault is clearly visible on the
earth's surface, appearing as a nasty scar in the
landscape.
The San Andreas is over 500 miles long and slices its
way past several major cities. It is among the most
active faults in the world and one of the most dangerous.
Scientists predict that a major earthquake will strike
here in the near future. That's why they want to learn
as much as they can about earthquakes.
25
This man isn't going for a hike. He's in the
mountains to install earthquake monitoring
equipment.
This device is called a seismometer. It detects
movement in the ground and sends out electronic
tones.
The tones may not sound like much to you or me, but
they do to computers which can decipher the tones
into meaningful information.
Hundreds of seismometers have been buried as part
of an earthquake-monitoring network.
The seismometers are connected to a central computer
miles away. Here, the tones are analyzed, and
provide scientists with important information about
surface movement in their area.
The symbols on this computer monitor represent the
locations of buried seismometers. The thin lines
represent faults. When an earthquake occurs,
scientists are able to pinpoint its exact location.
Computers also help scientists analyze the different
types of seismic waves that occur during an
earthquake.
The first waves that reach the surface are called P
waves. P waves compress and stretch the material
they travel through shown here in this model.
This can be more easily seen using a model with a
grid pattern. Here you can see that some sections of
the grid have been stretched and other sections have
been squeezed together.
26
The next waves that reach the surface are called S
waves. S waves produce an up and down rolling
motion in the earth's surface.
There are other types of waves as well, and a single
large earthquake can produce all of them.
By examining various wave patterns, scientists can
determine the strength of an earthquake, which is
referred to as its magnitude.
Earthquakes are assigned a number according to
magnitude. The numbering system is referred to as
the Richter scale. The larger the number, the greater
the earthquake's magnitude.
The Loma Prieta Earthquake of 1989 registered 7.1
on the Richter scale. Even though the epicenter was
60 miles away, damage in San Francisco and Oakland
was considerable. Had the epicenter been closer, the
damage to these cities could've been much worse,
and thousands of people might've been killed. The
closer large populations are to an earthquake's
epicenter, the greater likelihood there will be for death
and destruction.
A quake not much larger than the Loma Prieta quake
struck China in 1976. The epicenter, though, was
near a highly populated area and as many as 650,000
people were killed.
The most devastating earthquake to strike the United
States was the San Francisco earthquake of 1906.
Nearly 700 people were killed and the city center was
destroyed. Scientists believe another devastating
earthquake could strike a major city like San
Francisco or Los Angeles in the very near future; a
quake so large, it would have the potential of killing
thousands.
27
That's why some cities conduct readiness alerts that
simulate the kind of devastation that could occur, with
the hope of being better prepared.
That's why scientists study the damage caused by
earthquakes. In this way, they learn more about the
destructive capabilities of earthquakes and what can
be done to avoid such destruction in the future.
Scientists hope that one day they will be able to
forecast earthquakes in much the same way they can
forecast weather. So far, earthquake forecasting is
not very precise and people living in earthquake prone
areas are advised to expect an earthquake at any time.
The next major earthquake might not strike for years,
or it might strike within seconds.
In this program, we have seen how most earthquakes
are triggered by movements in the giant plates that
form a shell around the earth, and that most
earthquakes occur directly above the edges of these
moving plates.
Earthquakes can occur near divergent boundaries,
convergent boundaries, and transform boundaries.
We've seen that earthquakes occur when one side of a
fault suddenly slides past another. The energy that is
released is in the form of seismic waves which radiate
in all directions.
When these waves reach the surface, they can cause
considerable surface movement and destruction.
The place where a fault slips is called the earthquake's
focus, and the earth's surface directly above the focus
is called the epicenter.
We've seen that the first wave to reach the surface is
called a P wave, and the second wave is called an S
wave.
28
We've seen that scientists use instruments like
seismometers to record and measure these waves,
helping them determine when and where an
earthquake occurred and how powerful it was.
The strength of an earthquake is referred to as its
magnitude. Earthquake magnitudes are measured
according to the Richter scale.
We've seen the results of devastating earthquakes
around the world and learned that an earthquake's
destructive capability is greater near the epicenter.
While earthquakes are frightening, they serve to
remind us that our planet is in a constant state of
change.
While we may someday be able to forecast the
occurrence of earthquakes, we will never be able to
alter the great forces that are at work within our
planet.
29
CLOZE EVALUATION QUESTIONS
EARTHQUAKES: OUR RESTLESS PLANET
NAME ________
DIRECTIONS: Select the answer, from the four choices given, by circling the correct letter.
1. Our earth is an ever-changing place on which we live. Some sources of
this change are _______ . When one of these events happens, the effects can
be slight or very damaging, depending upon the force of it.
1.
A. geysers
B. earthquakes
C. hurricanes
D. volcanoes
2. In order to understand how earthquakes occur, it is necessary to look inside
the earth. The earth is made up of several different layers. The center layer is
called the inner core. Next is the outer core, followed by the ________ , which
is not as hot as these cores.
2.
A. mantle
B. crust
C. magma core
D. middle core
3. The uppermost layer of the earth is the region we live on. The _______
is this layer which is affected by what is happening beneath it. When earthquakes take place, the effect can cause great damage to buildings and property as well as injury and death to people.
3.
A. surface
B. mantle
C. crust
D. outside core
4. The crust would look quite different if we could strip away the oceans and
plant life. In many places the crust is cracked. These large pieces of the crust
are called _______ . The continents rest upon these pieces and have actual
ly moved over millions of years.
4.
A. plates
B. landforms
C. land masses
D. countries
5. The earth's huge plates have been moving very, very slowly. The move
ment is so slight that one cannot see it happening. Scientists believe that this
process of movement, called _______ , is a major cause of geological
5.
A. transformation
B. subduction
C. volcanism
D. continental drift
changes on the planet.
6.
We need to look below the surface to understand the causes of earth
quakes. Scientists believe that liquid matter in the mantle is circulating, or mov
ing. This causes the earth's plates to move. When plates move in opposite
directions, the spaces between them are called ________. Most of these are
located beneath the oceans.
6.
A. convergent boundaries
B. divergent boundaries
C. transform boundaries
D. fault lines
7. The grinding of the earth's plates has been going on for millions of years.
One result of this process is a crack in the earth's surface, called a ________ .
One side of this crack tries to move in one direction while the other side moves
in the opposite direction. The earth's plates remain locked in position until
stress from below forces them to move.
7.
A. fault
B. break
C. space
D. separation
8. An earthquake occurs when the stress below the surface causes areas on
both sides of the fault line to move. When this happens, the energy released is
in the form of _______ . If the disturbance is big enough, the force will even
tually cause damage to the surrounding areas.
8.
A. mantle waves
B. rock waves
C. seismic waves
D. tidal waves
9.
In the state of California there have been a number of earthquakes. The
most active earthquake area is along the _______ fault line. This fault line is
over 500 miles long and it is one of the most active and dangerous earthquake
zones on earth.
9.
A. LaJolla
B. San Jacinto
C. San Jose
D. San Andreas
10. Scientists record and study the movements of the earth's crust on a daily
basis. Earthquakes can be classified according to the ________ which mea
sures the intensity of the quake. A slight movement may register a 1 while an
earthquake in China in 1989 measured a 7.1 on the scale. Perhaps someday
scientists will be able to predict earthquakes with a high degree of accuracy.
10. A. Roenthen Scale
B. Richter Scale
C. Ranking Scale
D. Rigidity Scale
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