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Chapter

88Earthquakes and

Earth’s Interior

Chapter

8.1 8.1 ObjectivesObjectivesEarthquakes

1. Compare and Contrast the epicenter and focus of

an earthquake

2. Indentify the cause of earthquakes using the elastic

rebound hypothesis.

3. Explain what a fault is.

4. Compare and contrast aftershocks and foreshocks.

Earthquakes

6.1 What Is an Earthquake?

� earthquake

� vibration of Earth

�release of energy

� Focus

�Origin of Earthquake

� Epicenter

�Surface point directly above the focus

� Faults

�Fractures in E. where movement occurs

Focus, Epicenter, and Fault

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Slippage Along a Fault

Cause of Earthquakes

6.1 What Is an Earthquake?

���� Elastic Rebound Hypothesis

• rapid release of elastic energy

stored in rock

• When strength of rock is exceeded

it breaks

• Vibrations are caused by the break

Elastic Rebound Hypothesis

Cause of Earthquakes

6.1 What Is an Earthquake?

• Aftershock

• _____________________

• foreshock

•_______________________

� Aftershocks and Foreshocks

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Chapter

8.2 8.2 ObjectivesObjectivesMeasuring Quakes

1. Identify 3 types of seismic waves and know how

each moves.

2. Explain how to locate the epicenter of an

earthquake.

3. Describe the different ways a Quake is measured.

4. Know the difference between a seismograph and

seismogram.

Earthquake Waves

8.2 Measuring Earthquakes

���� Seismographs -

���� Seismograms -

Seismograph Seismogram

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3 types of Earthquake Waves

8.2 Measuring Earthquakes

• P waves

- Speed -__________________

- P

- Travel through ________ ___________ &

___________

Earthquake Waves

8.2 Measuring Earthquakes

• S waves

- Travel along outer surface

- Speed-

- Shake particles -

- Travel only through _____________

Types of Earthquake Waves

8.2 Measuring Earthquakes

3. Surface waves are seismic waves that

travel along Earth’s outer layer.

� A seismogram

� shows all three types of waves

Seismic Waves

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Locating an Earthquake

8.2 Measuring Earthquakes

• Locating Epicenter

• Using the difference in the arrival times

between P and S wave

• 3 seismographs are needed

• About 95 percent of the major earthquakes

occur in a few narrow zones.

Locating an Earthquake

Measuring Earthquakes

8.2 Measuring Earthquakes

• Two factors—

•Intensity

•magnitude

• Richter Scale- NOT USED BY SCIENTISTS

• Not good for large earthquakes

• Based on largest seismic wave

• 32-fold energy increase per #

Measuring Earthquakes

8.2 Measuring Earthquakes

���� Momentum Magnitude Scale

• amount of displacement

• Surface Area of Fault

• Size of Wave

• Only scale that estimates total Amount of energy released

• Measures very large earthquakes

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Earthquake Magnitudes Some Notable Earthquakes

Chapter

8.3 8.3 ObjectivesObjectivesMeasuring Quakes

1. Describe 4 factors that contribute to earthquake

destruction.

2. Explain 3 other dangers associated with

Earthquakes.

3. Explain the potential for earthquake prediction &

explain seismic gap.

4. Be able to calculate the earthquake probability for

various locations using the internet.

Seismic Vibrations

8.3 Destruction from Earthquakes

• Damage depends on

•Intensity

•Duration

•material on which the structure is built

•design of structure

• unreinforced stone & brick are worst

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Earthquake Damage

Seismic Vibrations

8.3 Destruction from Earthquakes

���� Liquefaction

• Saturated material turns fluid

• Underground objects may float to surface

Effects of Subsidence Due to

Liquefaction

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Effects of Subsidence Due to

Liquefaction

Tsunamis

8.3 Destruction from Earthquakes

���� Cause of Tsunamis

• tsunami

•slab of the ocean floor is displaced vertically

along a fault and wave results

•Can be caused by underwater landslide.

• Tsunami is the Japanese word for “seismic sea

wave.”

Movement of a Tsunami

Tsunamis

8.3 Destruction from Earthquakes

• Large earthquakes are reported to Hawaii from

Pacific seismic stations.

���� Tsunami Warning System

• Although tsunamis travel quickly, there is

sufficient time to evacuate all but the area

closest to the epicenter.

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Other Dangers

8.3 Destruction from Earthquakes

• Landslides

•Greatest damage

• Ground Subsidence

•Sinking of ground

•Caused by vibrations

• Fire

•San Francisco 1906

•Gas, electrical, water lines severed

Landslide Damage

Predicting Earthquakes

8.3 Destruction from Earthquakes

• Not yet possible

���� Short-Range Predictions

• NO predictions, only probabilities

���� Long-Range Forecasts

• seismic gap

•where there has not been any earthquake

activity for a long period of time.

Chapter

8.4 8.4 ObjectivesObjectivesEarth’s Layers

1. List the 3 main layers of earth based on

composition.

2. List & describe 5 layers of the Earth based on

physical properties.

3. Explain how Earthquakes help us understand the

Earth’s layers.

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Layers Defined by Composition

8.4 Earth’s Layered Structure

���� Three major zones

• Thin, rocky outer layer

���� Crust

• thickness varies

- 7 km in oceanic

- 8–40 km continental

- Exceeds 70 km in mountain

Layers Defined by Composition

8.4 Earth’s Layered Structure

���� Crust cont.

• Continental crust

- Upper - granitic rocks

- Lower - basaltic

- density is about 2.7 g/cm3

- Up to 4 billion years old

Layers Defined by Composition

8.4 Earth’s Layered Structure

���� Crust cont.

• Oceanic crust

- Basaltic composition

- Density about 3.0 g/cm3

- Younger (<180 million yrs)

Seismic Waves Paths Through the Earth

animation

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Layers Defined by Composition

8.4 Earth’s Layered Structure

���� Mantle• Below crust

• to a depth of 2900 kilometers

• Composition

•Upper mantle - peridiotite

Layers Defined by Composition

8.4 Earth’s Layered Structure

���� Core

• Below mantle

• Sphere with a radius of 3486 kilometers

• Composed of an iron-nickel alloy

• Average density of nearly 11 g/cm3

Layers Defined by Physical Properties

8.4 Earth’s Layered Structure

���� Lithosphere

• Crust and uppermost mantle (about 100 km thick)

• Cool, rigid, solid

���� Asthenosphere

• Beneath the lithosphere

• Upper mantle

• To a depth of about 660 kilometers

• Soft, weak layer that is easily deformed

Layers Defined by Physical Properties

8.4 Earth’s Layered Structure

���� Lower Mantle

• 660–2900 km

• More rigid layer

• Rocks are very hot and capable of gradual flow.

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Layers Defined by Physical Properties

8.4 Earth’s Layered Structure

���� Inner Core

• Sphere with a radius of 1216 km

• Behaves like a solid

���� Outer Core

• Liquid layer

• 2270 km thick

• Convective flow of metallic iron within generates Earth’s magnetic field

Earth’s Layered Structure

Discovering Earth’s Layers

8.4 Earth’s Layered Structure

• Velocity of seismic waves increases abruptly below

50 km of depth

• Separates crust from underlying mantle

���� Shadow Zone

• Absence of P waves from about 105 degrees to

140 degrees around the globe from an earthquake

• Can be explained if Earth contains a core composed of materials unlike the overlying mantle

���� Moho ˇ ´

Earth’s Interior Showing

P and S Wave Paths

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Discovering Earth’s Composition

8.4 Earth’s Layered Structure

���� Mantle

���� Crust• Early seismic data and drilling technology

indicate that the continental crust is mostly made

of lighter, granitic rocks.

• Composition is more speculative.

• Some of the lava that reaches Earth’s surface

comes from asthenosphere within.

Discovering Earth’s Composition

8.4 Earth’s Layered Structure

���� Core• Earth’s core is thought to be mainly dense iron

and nickel, similar to metallic meteorites. The

surrounding mantle is believed to be composed

of rocks similar to stony meteorites.