Earthquakes Chap. 19 Forces within the Earth Seismic Waves Measuring and Locating Earthquakes Earthquakes and Society Kobe, Japan

Forces within the Earth – 19.1 Objectives define stress and strain as they apply to rocks distinguish among the three types of faults Contrast three types of seismic waves Fault scarp

I.Physics and Forces

A.Stress – the force per unit area

I.Physics and Forces A.Stress – the force per unit area 1.Compression – decreases the volume.

I.Physics and Forces A.Stress – the force per unit area 1.Compression – decreases the volume. 2.Tension – pulls apart.

I.Physics and Forces A.Stress – the force per unit area 1.Compression – decreases the volume. 2.Tension – pulls apart. 3.Shear – twists.

I.Physics and Forces B.Strain – deformation due to stress

I.Physics and Forces B.Strain – deformation due to stress 1.Compression Strain

I.Physics and Forces B.Strain – deformation due to stress 1.Compression Strain 2.Tensional Strain

I.Physics and Forces B.Strain – deformation due to stress 1.Compression Strain 2.Tensional Strain 3.Shear Strain

I.Physics and Forces C.Stress/Strain Curve

I.Physics and Forces D.Deformation – altering the shape 1.When too much stress is applied, permanent deformation occurs.

I.Physics and Forces D.Deformation – 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. Faults Fracture of system of fractures in the Earth’s crust along which movement occurs. Taiwan – fault line running through rice paddy

II. Faults A.Reverse Faults – faults caused by horizontal compression

II. Faults B.Normal Faults – faults caused by horizontal tension

II. Faults C.Strike Slip – faults caused by horizontal shear

III. Earthquake Waves A.Primary (P) waves Compression (squeeze and pull) waves. Compression occurs in the same direction as the wave travels. Wave travels underground (a body wave)

III. Earthquake Waves B.Secondary (S) waves Displaces particles at a right angle to the wave motion. Wave travels underground (a body wave)

III. Earthquake Waves C.Surface Wave Particles move up/down and side/side. Wave travels at the surface.

IV. Earthquake ‘Anatomy’ A.Focus – point where an earthquake originates (often underground)

IV. Earthquake ‘Anatomy’ B.Epicenter – Point on Earth’s surface directly above the focus.

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Seismic Waves – 19.2 Objectives Describe how a seismometer works Explain how seismic waves have been used to determine the structure and composition of Earth’s interior.

I.Seismometer

A.How does it work?

I.Seismometer A.How does it work? B.What is it used for?

I.Seismometer A.How does it work? B.What is it used for? C.What does its output look like?

Can you label the waves?

II.Travel-Time Curves

A.Scientists have measured the time it takes seismic waves to travel.

II.Travel-Time Curves A.Scientists have measured the time it takes seismic waves to travel. B.The graph.

III. The Earth’s Interior

A.The path of P-waves is linear when traveling in the mantle.

III. The Earth’s Interior A.The path of P-waves is linear when traveling in the mantle. B.The path of P-waves is bent when it enters a different material.

III. The Earth’s Interior A.The path of P-waves is linear when traveling in the mantle. B.The path of P-waves is bent when it enters a different material. C. S-waves cannot travel through liquids.

What does the s-wave shadow indicate? Why is there a p-wave shadow? The Earth’s Interior

IV. The Earth’s Composition

A.Lithosphere (crust and top layer of mantle) is primarily igneous rocks (granite, basalt, and peridotite).

IV. The Earth’s Composition A.Lithosphere (crust and top layer of mantle) is primarily igneous rocks (granite, basalt, and peridotite). B.The asthenosphere (partially melted mantle) is peridotite.

IV. The Earth’s Composition A.Lithosphere (crust and top layer of mantle) is primarily igneous rocks (granite, basalt, and peridotite). B.The asthenosphere (partially melted mantle) is peridotite. C.The lower mantle is solid, made of iron, silicon and magnesium oxides.

IV. The Earth’s Composition A.Lithosphere (crust and top layer of mantle) is primarily igneous rocks (granite, basalt, and peridotite). B.The asthenosphere (partially melted mantle) is peridotite. C.The lower mantle is solid, made of iron, silicon and magnesium oxides. D.The core is dense iron & nickel.

Challenge Problem The earth’s core has a radius of 3450 km and a density of 12,500 kg/m 3. The earth’s core has a radius of 3450 km and a density of 12,500 kg/m 3. The earth’s mantle has a radius of 6371 km and a density of 4200 kg/m 3. The earth’s mantle has a radius of 6371 km and a density of 4200 kg/m 3. V sphere = 4/3 πr 3 V sphere = 4/3 πr 3 1 km = 1000 m 1 km = 1000 m What is the Earth’s core volume? What is the volume of Earth’s mantle?

Measuring and Locating Earthquakes

I.Magnitude and Intensity

The energy of an earthquake’s waves A.The scale measures the magnitude of an earthquake.

I.Magnitude and Intensity Considers various seismic waves, size of fault rupture, amount of movement, and rocks’ stiffness A.The Richter scale measures the magnitude of an earthquake. B.The scale also measures an earthquake’s magnitude.

I.Magnitude and Intensity A.The Richter scale measures the magnitude of an earthquake. B.The Moment Magnitude scale also measures an earthquake’s magnitude. Considers various seismic waves, size of fault rupture, amount of movement, and rocks’ stiffness

I.Magnitude and Intensity C.The scale measures the amount of damage.

I.Magnitude and Intensity C.The modified Mercalli scale measures the amount of damage.

II. Locations of earthquakes

A.The depth of focus determines the damage of an earthquake. The deeper the focus, the less damage

II. Locations of earthquakes A.The depth of focus determines the damage of an earthquake. B.Earthquake distance is found using the separation time for and ____ __.

II. Locations of earthquakes A.The depth of focus determines the damage of an earthquake. B.Earthquake distance is found using the separation time for S waves and P waves.

II. Locations of earthquakes C.Data from at least three stations is combined by a method called triangulation.

II. Locations of earthquakes C.Seismic Belts – Earthquakes are plotted on a world map.

II. Locations of earthquakes C.Seismic Belts – Earthquakes are plotted on a world map.

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Earthquakes and Society

I.Structural Damage

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

A.Buildings made of ______, _______, or ______ experience significant damage. B.Buildings of a certain ______ experience significant damage. I.Structural Damage

A.Buildings made of ______, _______, or ______ experience significant damage. B.Buildings of a certain ______ experience significant damage. C.Earthquakes may cause ______ when soil is liquified. I.Structural Damage

Liquefaction Process where soil strength is reduced by earthquake shaking.

I.Structural Damage D.Earthquakes may cause fault scarps.

I.Structural Damage D.Earthquakes may cause fault scarps. E.Offshore quakes may cause ________, or large waves.

F.High risk areas

II. Predicting Earthquakes

A.Earthquake history – look at past pattern. There is a seismic gap on San Andreas Fault – last major earthquake in 1906.

II. Predicting Earthquakes A.Earthquake history – look at past pattern. There is a seismic gap on San Andreas Fault – last major earthquake in B.Measure accumulated strain.

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