EarthquakesEarthquakesChap. 19Chap. 19Chap. 19Chap. 19

Forces within the Earth

Seismic Waves

Measuring and Locating Earthquakes

Earthquakes and Society

Kobe, Japan

Forces within the Earth – 19.1

ObjectivesObjectives• define stress and strain as they apply to rocks• distinguish among the three types of faults• Contrast three types of seismic waves

Fault scarpFault scarp

I.I. Physics and ForcesPhysics and Forces

I.I. Physics and ForcesPhysics and ForcesA.A. Stress – the force per unit areaStress – the force per unit area

I.I. Physics and ForcesPhysics and ForcesA.A. Stress – the force per unit areaStress – the force per unit area

1. Compression – decreases the volume.

I.I. Physics and ForcesPhysics and ForcesA.A. Stress – the force per unit areaStress – the force per unit area

1. Compression – decreases the volume.

2. Tension – pulls apart.

I.I. Physics and ForcesPhysics and ForcesA.A. Stress – the force per unit areaStress – the force per unit area

1. Compression – decreases the volume.

2. Tension – pulls apart.

3. Shear – twists.

I.I. Physics and ForcesPhysics and ForcesB.B. Strain – deformation due to stressStrain – deformation due to stress

I.I. Physics and ForcesPhysics and ForcesB.B. Strain – deformation due to stressStrain – deformation due to stress

1. Compression Strain

I.I. Physics and ForcesPhysics and ForcesB.B. Strain – deformation due to stressStrain – deformation due to stress

1. Compression Strain

2. Tensional Strain

I.I. Physics and ForcesPhysics and ForcesB.B. Strain – deformation due to stressStrain – deformation due to stress

1. Compression Strain

2. Tensional Strain

3. Shear Strain

I.I. Physics and ForcesPhysics and ForcesC.C. Stress/Strain CurveStress/Strain Curve

I.I. Physics and ForcesPhysics and ForcesD.D. Deformation – altering the shapeDeformation – altering the shape

1. When too much stress is applied, permanent deformation occurs.

I.I. Physics and ForcesPhysics and ForcesD.D. Deformation – altering the shapeDeformation – altering the shape

1. When too much stress is applied, permanent deformation occurs.

2. Brittle objects cannot withstand much stress before they are deformed.

II.II. FaultsFaults

Fracture of system of fractures in the Earth’s crust along which movement occurs.

Taiwan – fault line running through rice paddy

II.II. FaultsFaultsA.A. Reverse Faults – faults caused by Reverse Faults – faults caused by

horizontal compressionhorizontal compression

II.II. FaultsFaultsB.B. Normal Faults – faults caused byNormal Faults – faults caused by

horizontal tensionhorizontal tension

II.II. FaultsFaultsC.C. Strike Slip – faults caused by Strike Slip – faults caused by

horizontal shearhorizontal shear

III.III. Earthquake WavesEarthquake WavesA.A. Primary (P) wavesPrimary (P) waves

Compression (squeeze and pull) waves. Compression occurs in the same direction as the wave travels.

Wave travels underground (a body wave)

III.III. Earthquake WavesEarthquake WavesB.B. Secondary (S) wavesSecondary (S) waves

Displaces particles at a right angle to the wave motion.

Wave travels underground (a body wave)

III.III. Earthquake WavesEarthquake WavesC.C. Surface WaveSurface Wave

Particles move up/down and side/side.

Wave travels at the surface.

IV.IV. Earthquake ‘Anatomy’Earthquake ‘Anatomy’A.A. Focus – point where an Focus – point where an

earthquake originates (often earthquake originates (often underground)underground)

IV.IV. Earthquake ‘Anatomy’Earthquake ‘Anatomy’B.B. Epicenter – Point on Earth’s Epicenter – Point on Earth’s

surface directly above the focus.surface directly above the focus.

The End

Seismic Waves – 19.2

ObjectivesObjectives• Describe how a seismometer works• Explain how seismic waves have been used to determine the structure and composition of Earth’s interior.

I.I. SeismometerSeismometer

I.I. SeismometerSeismometerA.A. How does it work?How does it work?

I.I. SeismometerSeismometerA.A. How does it work?How does it work?

B.B. What is it used for?What is it used for?

I.I. SeismometerSeismometerA.A. How does it work?How does it work?

B.B. What is it used for?What is it used for?

C.C. What does its output look like?What does its output look like?

Can you label the waves?Can you label the waves?

Can you label the waves?Can you label the waves?

II.II.Travel-Time CurvesTravel-Time Curves

II.II.Travel-Time CurvesTravel-Time CurvesA.A. Scientists have measured the time Scientists have measured the time

it takes seismic waves to travel.it takes seismic waves to travel.

II.II.Travel-Time CurvesTravel-Time CurvesA.A. Scientists have measured the time Scientists have measured the time

it takes seismic waves to travel.it takes seismic waves to travel.

B.B. The graph.The graph.

III.III. The Earth’s InteriorThe Earth’s Interior

III.III. The Earth’s InteriorThe Earth’s InteriorA.A. The path of P-waves is linear The path of P-waves is linear

when traveling in the mantle.when traveling in the mantle.

III.III. The Earth’s InteriorThe Earth’s InteriorA.A. The path of P-waves is linear The path of P-waves is linear

when traveling in the mantle.when traveling in the mantle.

B.B. The path of P-waves is bent when The path of P-waves is bent when it enters a different material.it enters a different material.

III.III. The Earth’s InteriorThe Earth’s InteriorA.A. The path of P-waves is linear The path of P-waves is linear

when traveling in the mantle.when traveling in the mantle.

B.B. The path of P-waves is bent when The path of P-waves is bent when it enters a different material.it enters a different material.

C.C. S-waves cannot travel through S-waves cannot travel through liquids.liquids.

What does the s-wave shadow indicate?

Why is there a p-wave shadow?

The Earth’s InteriorThe Earth’s Interior

IV.IV. The Earth’s CompositionThe Earth’s Composition

IV.IV. The Earth’s CompositionThe Earth’s CompositionA.A. Lithosphere (crust and top layer of Lithosphere (crust and top layer of

mantle) is primarily igneous rocks mantle) is primarily igneous rocks (granite, basalt, and peridotite).(granite, basalt, and peridotite).

IV.IV. The Earth’s CompositionThe Earth’s CompositionA.A. Lithosphere (crust and top layer of Lithosphere (crust and top layer of

mantle) is primarily igneous rocks mantle) is primarily igneous rocks (granite, basalt, and peridotite).(granite, basalt, and peridotite).

B.B. The asthenosphere (partially melted The asthenosphere (partially melted mantle) is peridotite.mantle) is peridotite.

IV.IV. The Earth’s CompositionThe Earth’s CompositionA.A. Lithosphere (crust and top layer of Lithosphere (crust and top layer of

mantle) is primarily igneous rocks mantle) is primarily igneous rocks (granite, basalt, and peridotite).(granite, basalt, and peridotite).

B.B. The asthenosphere (partially melted The asthenosphere (partially melted mantle) is peridotite.mantle) is peridotite.

C.C. The lower mantle is solid, made of The lower mantle is solid, made of iron, silicon and magnesium oxides.iron, silicon and magnesium oxides.

IV.IV. The Earth’s CompositionThe Earth’s CompositionA.A. Lithosphere (crust and top layer of Lithosphere (crust and top layer of

mantle) is primarily igneous rocks mantle) is primarily igneous rocks (granite, basalt, and peridotite).(granite, basalt, and peridotite).

B.B. The asthenosphere (partially melted The asthenosphere (partially melted mantle) is peridotite.mantle) is peridotite.

C.C. The lower mantle is solid, made of The lower mantle is solid, made of iron, silicon and magnesium oxides.iron, silicon and magnesium oxides.

D.D. The core is dense iron & nickel.The core is dense iron & nickel.

Challenge ProblemChallenge Problem

• The earth’s core has a radius of 3450 The earth’s core has a radius of 3450 km and a density of 12,500 kg/mkm and a density of 12,500 kg/m33..

• The earth’s mantle has a radius of The earth’s mantle has a radius of 6371 km and a density of 4200 kg/m6371 km and a density of 4200 kg/m33. .

• VVspheresphere = 4/3 = 4/3 ππrr33

• 1 km = 1000 m1 km = 1000 m

What is the Earth’s core volume? What is What is the Earth’s core volume? What is the volume of Earth’s mantle?the volume of Earth’s mantle?

Measuring and Locating Earthquakes

I.I. Magnitude and IntensityMagnitude and Intensity

I.I. Magnitude and IntensityMagnitude and Intensity

The energy of an earthquake’s waves

A.A. The The scale measures the scale measures the magnitude of an earthquake.magnitude of an earthquake.

I.I. Magnitude and IntensityMagnitude and Intensity

Considers various seismic waves, size of fault rupture, amount of movement, and rocks’ stiffness

A.A. The The RichterRichter scale measures the scale measures the magnitude of an earthquake.magnitude of an earthquake.

B.B. The The scale also scale also measures an earthquake’s measures an earthquake’s magnitude.magnitude.

I.I. Magnitude and IntensityMagnitude and IntensityA.A. The The RichterRichter scale measures the scale measures the

magnitude of an earthquake.magnitude of an earthquake.

B.B. The The MomentMoment MagnitudeMagnitude scale also scale also measures an earthquake’s measures an earthquake’s magnitude.magnitude.

Considers various seismic waves, size of fault rupture, amount of movement, and rocks’ stiffness

I.I. Magnitude and IntensityMagnitude and IntensityC.C. The The scale scale

measures the amount of damage.measures the amount of damage.

I.I. Magnitude and IntensityMagnitude and IntensityC.C. The The modifiedmodified MercalliMercalli scale scale

measures the amount of damage.measures the amount of damage.

II.II. Locations of earthquakesLocations of earthquakes

II.II. Locations of earthquakesLocations of earthquakesA.A. The depth of focus determines the The depth of focus determines the

damage of an earthquake.damage of an earthquake.

The deeper the focus, the less damage

II.II. Locations of earthquakesLocations of earthquakesA.A. The depth of focus determines the The depth of focus determines the

damage of an earthquake.damage of an earthquake.

B.B. Earthquake distance is found using Earthquake distance is found using the separation time for the separation time for and and ____ __ ____ __..

II.II. Locations of earthquakesLocations of earthquakesA.A. The depth of focus determines the The depth of focus determines the

damage of an earthquake.damage of an earthquake.

B.B. Earthquake distance is found using Earthquake distance is found using the separation time for the separation time for S wavesS waves and and P wavesP waves..

II.II. Locations of earthquakesLocations of earthquakesC.C. Data from at least three stations is Data from at least three stations is

combined by a method called combined by a method called triangulation.triangulation.

II.II. Locations of earthquakesLocations of earthquakesC.C. Seismic Belts – Earthquakes are Seismic Belts – Earthquakes are

plotted on a world map.plotted on a world map.

II.II. Locations of earthquakesLocations of earthquakesC.C. Seismic Belts – Earthquakes are Seismic Belts – Earthquakes are

plotted on a world map.plotted on a world map.

The End

Earthquakes and Society

I.I. Structural DamageStructural Damage

A.A. Buildings made of ______ , Buildings made of ______ , _______ , or ______ experience _______ , or ______ experience significant damage.significant damage.

I.I. Structural DamageStructural Damage

A.A. Buildings made of ______ , Buildings made of ______ , _______ , or ______ experience _______ , or ______ experience significant damage.significant damage.

B.B. Buildings of a certain ______ Buildings of a certain ______ experience significant damage.experience significant damage.

I.I. Structural DamageStructural Damage

A.A. Buildings made of ______ , Buildings made of ______ , _______ , or ______ experience _______ , or ______ experience significant damage.significant damage.

B.B. Buildings of a certain ______ Buildings of a certain ______ experience significant damage.experience significant damage.

C.C. Earthquakes may cause ______ Earthquakes may cause ______ when soil is liquified.when soil is liquified.

I.I. Structural DamageStructural Damage

LiquefactionLiquefactionProcess where soil strength is Process where soil strength is reduced by earthquake shaking.reduced by earthquake shaking.

I.I. Structural DamageStructural DamageD.D. Earthquakes may cause fault Earthquakes may cause fault

scarps.scarps.

I.I. Structural DamageStructural DamageD.D. Earthquakes may Earthquakes may

cause fault scarps.cause fault scarps.

E.E. Offshore quakes Offshore quakes may cause may cause ________, or large ________, or large waves.waves.

F.F. High risk areasHigh risk areas

II.II. Predicting EarthquakesPredicting Earthquakes

II.II. Predicting EarthquakesPredicting EarthquakesA.A. Earthquake history – look at Earthquake history – look at

past pattern. There is a seismic past pattern. There is a seismic gap on San Andreas Fault – gap on San Andreas Fault – last major earthquake in 1906.last major earthquake in 1906.

II.II. Predicting EarthquakesPredicting EarthquakesA.A. Earthquake history – look at Earthquake history – look at

past pattern. There is a seismic past pattern. There is a seismic gap on San Andreas Fault – gap on San Andreas Fault – last major earthquake in 1906.last major earthquake in 1906.

B.B. Measure accumulated strain. Measure accumulated strain.

The End