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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 DayJoke of the Day

What did the ground say to the What did the ground say to the earthquake?earthquake?You crack me up.You crack me up.

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Earthquake H

azards

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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.ShockWave-StructureDesign.mov

..\..\..\Desktop\Power point clips\2.Building_Strength-Demo.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_Seismic_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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..\..\..\Desktop\Power point clips\Tsunami_Runup-ARSC.mov

..\..\..\Desktop\Power point clips\Tsunami_underwater.mov

Tsunami Animation

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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