Earthquakes and 8 Earth s Interior 8.1 ObjectivesO 8.2 Measuring Earthquakes ¢â‚¬¢ Locating Epicenter

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    Chapter

    88 Earthquakes and

    Earth’s Interior

    Chapter

    8.1 8.1 ObjectivesObjectives Earthquakes

    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 ObjectivesObjectives Measuring 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 ObjectivesObjectives Measuring 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 ObjectivesObjectives Earth’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 (

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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.