Download Unit 4 Lesson 8

Unit 4 Lesson 8 Earthquakes
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Unit 4 Lesson 8 Earthquakes
Indiana Standards
• 7.2.4 Explain how convection currents in the
mantle cause lithospheric plates to move causing
fast changes like earthquakes and volcanic
eruptions, and slow changes like creation of
mountains and formation of new ocean floor.
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What do we know?
• Earth is divided into tectonic plates that
are constantly moving
• Motion is caused by convection, slab
pull, and ridge push.
• Movements of tectonic plates cause
changes to earth’s surface
• These changes can form faults,
mountains, and earthquakes
What do we want to find out?
•
•
•
•
What is an earthquake?
What causes them?
Where do they occur?
What kind of damage results from
them?
Unit 4 Lesson 8 Earthquakes
Let’s Focus
What is an earthquake?
• Earthquakes are ground movements that occur
when blocks of rock in Earth move suddenly and
release energy.
• The energy is released as seismic waves that
cause the ground to move.
• 3 million earthquakes occur every year
• That equals to 1 earthquake every 10
seconds!!
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Unit 4 Lesson 8 Earthquakes
What is an earthquake?
• The place within Earth
where the first motion
occurs is called the
focus.
• The place on Earth’s
surface above the focus is
called the epicenter.
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Unit 4 Lesson 8 Earthquakes
What causes earthquakes?
• Most earthquakes occur near a tectonic plate
boundary, which is where two or more tectonic
plates meet.
• The movement of tectonic plates breaks Earth’s
crust into a series of faults, which are breaks in
Earth’s crust along which blocks of rocks move.
• The release of energy that accompanies the
movement of rock along a fault is what causes an
earthquake.
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Unit 4 Lesson 8 Earthquakes
What causes earthquakes?
• Stress causes deformation, which is the process
by which rock changes shape.
• As stress on rock increases, the energy stored in it
increases.
• When the stress is released, the rock sometimes
returns to its original shape.
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Unit 4 Lesson 8 Earthquakes
What causes earthquakes?
• Deformation in which rock can spring back to its
original shape is called elastic deformation.
• The return of rock to its original shape after
elastic deformation is called elastic rebound.
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Measuring the Magnitude
• Magnitude is a measure of the amount of energy
released by an earthquake
• 2 main scales are used:
• Richter Scale and Moment Magnitude
Unit 4 Lesson 8 Earthquakes
Unstable Ground
Where do earthquakes happen?
• Most earthquakes happen at or near tectonic plate
boundaries.
• At tectonic plate boundaries, stress builds up from
tectonic plates colliding, separating, or grinding
past each other.
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Earthquake hazards in USA
Earthquakes hazards all over
the world
Unit 4 Lesson 8 Earthquakes
Where do earthquakes happen?
• At divergent boundaries, tension stress causes
normal faults to form.
• Earthquakes tend to be shallow because the crust
is thin.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 4 Lesson 8 Earthquakes
Where do earthquakes happen?
• At convergent boundaries, rock is squeezed,
causing reverse faults to form.
• Earthquakes can be very strong and deep.
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Unit 4 Lesson 8 Earthquakes
Where do earthquakes happen?
• At transform boundaries, shear stress pushes
tectonic plates in opposite directions.
• Earthquakes tend to be relatively shallow.
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Unit 4 Lesson 8 Earthquakes
What are some effects of earthquakes?
• Most earthquakes do not cause damage, but some
strong earthquakes can cause major damage and
loss of life, especially in areas closest to the
epicenter.
• When the shaking of an earthquake is more than
structures can withstand, major destruction can
occur.
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What are some effects of earthquakes?
• Much of the injury and loss of life after an
earthquake is caused by structures that
collapse.
• Effects include: liquefaction, tsunami,
aftershocks, and fires.
Liquefaction
• Result from severe
ground shaking
• Buildings collapse
Aftershocks and fires
• After a large
earthquake, the number
of aftershocks can be
as frequent as 1000 per
day
• Gas lines are damaged
by shaking causing fires
and explosions
Unit 4 Lesson 8 Earthquakes
Tsunamis
• An earthquake under the ocean causes a vertical
movement of the seafloor that displaces a large
amount of water.
• A tsunami is a series of extremely long waves that
can travel across the ocean at speeds of up to
800 km/h.
• As the waves reach the shoreline, the height of
the waves increases. The huge waves can cause
major destruction.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 4 Lesson 8 Earthquakes
Killer Quake
• In 2004, an earthquake generated a tsunami that
wiped out half the population in Banda Aceh,
Indonesia.
• The tsunami traveled outward from the epicenter
in the Indian Ocean. Banda Aceh was very close to
the epicenter.
• The tsunami affected coastal areas around the
entire Indian Ocean, even reshaping many
coastlines in Asia.
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Earthquake safety
• DROP to the ground; take COVER by getting under a sturdy
table or other piece of furniture; and HOLD ON until the shaking
stops. If there isn’t a table or desk near you, cover your face and
head with your arms and crouch in an inside corner of the
building.
• Stay away from glass, windows, outside doors and walls, and
anything that could fall, such as lighting fixtures or furniture.
• Stay in bed if you are there when the earthquake strikes. Hold
on and protect your head with a pillow, unless you are under a
heavy light fixture that could fall. In that case, move to the
nearest safe place.
Earthquake Safety
• Do not use a doorway except if you know it is a
strongly supported, load-bearing doorway and it is
close to you. Many inside doorways are lightly
constructed and do not offer protection..
• Stay inside until the shaking stops and it is safe to go
outside. Do not exit a building during the shaking.
Research has shown that most injuries occur when
people inside buildings attempt to move to a different
location inside the building or try to leave.