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7.3
Earthquakes and
Society
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Have you experienced an
earthquake? How did you feel?
What did you do to protect yourself?
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Earthquake Hazard
•A measurement of how likely an area is to have
damaging earthquakes in the future
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Joke of the Day
What did the ground say to the
earthquake?
You crack me up.
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Earthquake Hazards
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What is the relationship between the
strength of earthquakes and the
frequency with which they happen?
Strong earthquakes occur much less often
than small earthquakes do. This
relationship is the result of the amount of
energy released by each size of
earthquake.
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Seismic gaps
•Area along a fault where few earthquakes happen
•Scientist predict that larger earthquakes will happen
here due to build up of stress
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Reducing Earthquake Damage
•Retrofitting – making old structures more resistant to
earthquakes
Example: securely fasten the building to its
foundation
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Cross braces
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Structures
..\..\..\Desktop\Power point
clips\1.ShockWaveStructureDesign.mov
..\..\..\Desktop\Power point
clips\2.Building_StrengthDemo.mov
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How does building construction relate to
the damage that earthquakes can cause?
Structures that are equipped with
earthquake-resistant technology or that
have been retrofitted are much better able
to withstand the ground shaking that is
generated by earthquakes.
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Retrofitting
..\..\video clips\7.3 Earthquakes and
Society\Investigating_Earthquakes__Protecting_Structures_Against_S
eismic_Waves.asf
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Are you prepared for an
Earthquake?
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How do earthquakes change human
habitats?
Earthquakes can collapse structures, start
fires, damage infrastructure, such as
waterlines, power lines, gas lines, and
roadways, and trigger landslides.
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Family Plan
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Safety Plan
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Tsunamis
•An extremely long wave that can travel across the ocean.
•Caused by earthquakes on the ocean floor.
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Tsunamis
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How do tsunamis form?
Tsunamis form when an undersea
earthquake causes a vertical movement
of the sea floor. This movement displaces
an enormous volume of water, which
creates a series of tsunami waves.
Volcanic eruptions, landslides, and
meteorite impacts can also trigger
tsunamis.
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Tsunami Animation
..\..\..\Desktop\Power point clips\Tsunami_Runup-ARSC.mov
..\..\..\Desktop\Power point clips\Tsunami_underwater.mov
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Tsunamis
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Review Questions
1.Describe the seismic gap hypothesis.
According to the seismic gap
hypothesis, sections of active faults that
have had relatively few recent earthquakes
are likely to be the sites strong
earthquakes sometime in the future.
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2. Compare four examples of technologies that are
designed to make buildings earthquake resistant.
A mass damper is a computer-controlled weight that
is placed in the roof of a building to counteract the
building’s movement. Base isolators at the base of
the building absorb seismic waves and prevent the
waves from traveling through the building. Steel cross
braces counteract pressure that pushes and pulls at
the side fo a building during an earthquake. Pipes
that have flexible joints are able ot bend and twist
during an earthquake.
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3. Explain how the transfer of energy as seismic waves is
related to the frequency and magnitude of earthquakes in
a region.
When large earthquakes happen, a huge amount of
energy is released as seismic waves. Many smaller
earthquakes are required to release this same amount of
energy as seismic waves.
4. How do earthquakes and tsunamis change human and
wildlife habitats?
Earthquakes can damage buildings, bridges, and roads;
start fires; and cause landslides. Tsunamis can generate
large waves that flood large areas of coastline, causing
large amounts of damage and loss of life.
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Review 7.3
•Seismic gap
•Mass damper
•Earthquake hazard
•Flexible pipe
•Tsunami
•Base isolator
•Retrofitting
•Frequency
•Cross brace
•Active tendon system
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