Table of Contents

Earthquakes

Forces in Earth’s Crust

Earthquakes and Seismic Waves

Monitoring Earthquakes

Earthquake Safety

Table of Contents

Earthquakes

Plate Tectonic Boundaries

Earthquakes

Forces in Earth’s Crust

•How does stress in the crust change Earth’s surface?

•Where are faults usually found, & why do they form?

•What land features result from the forces of plate movement?

Earthquakes

Stress• The movement of Earth’s plates create enormous forces that

squeeze or pull the rock in the crust

• A force that acts on rock to change its shape or volume is stress.

• Stress adds energy to the rock

• The energy is stored in the rock until it changes shape or breaks

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3 Kinds of Stress in Earth’s Crust1. Tension- pulls on the crust, stretching rock so that

becomes thinner in the middle.

2. Compression-squeezes rock until it folds or breaks.

3. Shearing-pushes a mass of rock in two opposite directions

Earthquakes - Forces in Earth’s Crust

Types of StressThe stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.

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Types of StressThe stress force called compression squeezes rock until it folds or breaks.

- Forces in Earth’s Crust

Earthquakes

Types of StressStress that pushes a mass of rock in two opposite directions is called shearing.

- Forces in Earth’s Crust

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Faults• When enough stress builds up in rock, the rock

breaks, creating a fault.

• A fault is a break in the rock of the crust where rock surfaces slip past each other

• Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks

• There are three main types of faults: Normal faults, reverse faults, & strike-slip faults

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Kinds of FaultsTension in Earth’s crust pulls rock apart, causing normal faults.

- Forces in Earth’s Crust

Earthquakes

Normal Fault

• Tension causes a normal fault. In a normal fault, the fault is at an angle, & one block of rock lies above the fault while the other block lies below the fault.

• The block of rock that lies above is called the hanging wall.• The rock that lies below is called the footwall.

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Kinds of FaultsA reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

- Forces in Earth’s Crust

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Reverse FaultsCompression causes reverse faults.A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

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Kinds of FaultsIn a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up and down motion.

- Forces in Earth’s Crust

Earthquakes

Strike-Slip Fault

Shearing creates strike-slip faults.

In a strike-slip fault, the rocks on either side of the fault slip past each sideways, with little up or down motion.

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Anticlines & Synclines

• Found on many parts of the Earth’s surface where compression forces have folded the crust

• The collision of two plates can cause compression & folding of the crust over a wide area

• Where two normal faults cut through a block of rock, fault movements may push up a fault-block mountain.

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Changing Earth’s SurfaceOver millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus.

- Forces in Earth’s Crust

Earthquakes

LandformsOver millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines & synclines, folded mountains, fault-block mountains, and plateaus.

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AnticlineA fold in rock that bends upward into an arch is an anticline.

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SynclinesA fold in rock that bends downward to form a valley is a syncline.

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Plateaus

• The forces that raise mountains can also uplift, or raise plateaus.

• A plateau is a large area of flat land elevated high above sea level.

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Colorado Plateau

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Changing Earth’s SurfaceOver millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus.

- Forces in Earth’s Crust

Earthquakes

Building VocabularyA definition states the meaning of a word or phrase. As you read, write a definition of each Key Term in your own words.

Key Terms: Examples:

- Forces in Earth’s Crust

stress Stress is a force that acts on rock to change its shape or volume.

tension The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.

compression The stress force called compression squeezes rock until it folds or breaks.

shearing Stress that pushes a mass of rock in two opposite directions is called shearing.

normal fault Tension in Earth’s crust pulls rock apart, causing normal faults.

reverse fault A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

Key Terms: Examples:hanging wall

footwall

strike-slip fault

anticline

syncline

plateau

The block of rock that lies above a normal fault is called the hanging wall.The rock that lies below is called the footwall.In a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up or down motion.

A fold in rock that bends upward into an arch is an anticline.

A fold in rock that bends downward to form a valley is a syncline.

A plateau is a large area of flat land elevated high above sea level.

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End of Section:Forces in Earth’s

Crust

Earthquakes

Types of Seismic WavesSeismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface.

- Earthquakes and Seismic Waves

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Types of Seismic WavesP waves are seismic waves that compress and expand the ground like an accordion. S waves are seismic waves that vibrate from side to side as well as up and down.

- Earthquakes and Seismic Waves

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Types of Seismic WavesSurface waves move more slowly than P waves and S waves, but they produce the most severe ground movements.

- Earthquakes and Seismic Waves

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Measuring EarthquakesThe Mercalli scale was developed to rate earthquakes according to the amount of damage at a given place.

- Earthquakes and Seismic Waves

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Seismic Wave Speeds

Seismographs at five observation stations recorded the arrival times of the P and S waves produced by an earthquake. These data are shown in the graph.

- Earthquakes and Seismic Waves

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Seismic Wave Speeds

X-axis––distance from the epicenter; y-axis––arrival time.

Reading Graphs:

What variable is shown on the x-axis of the graph? The y-axis?

- Earthquakes and Seismic Waves

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Seismic Wave Speeds

7 minutes

Reading Graphs:

How long did it take the S waves to travel 2,000 km?

- Earthquakes and Seismic Waves

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Seismic Wave Speeds

4 minutes

Estimating:

How long did it take the P waves to travel 2,000 km?

- Earthquakes and Seismic Waves

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Seismic Wave Speeds

2,000 = 3.5 minutes4,000 = 4.5 minutes

Calculating:

What is the difference in the arrival times of the P waves and the S waves at 2,000 km? At 4,000 km?

- Earthquakes and Seismic Waves

Earthquakes

Locating the EpicenterGeologists use seismic waves to locate an earthquake’s epicenter.

- Earthquakes and Seismic Waves

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Main Idea

Detail Detail Detail

Identifying Main IdeasAs you read the section “Types of Seismic Waves,” write the main idea in a graphic organizer like the one below. Then write three supporting details. The supporting details further explain the main idea.

Seismic waves carry the energy of an earthquake.

P waves compress and expand the

ground.

S waves vibrate from side to side as well as up and

down.

Surface waves produce the most

severe ground movements.

- Earthquakes and Seismic Waves

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End of Section:Earthquakes and Seismic Waves

Earthquakes

The Modern SeismographSeismic waves cause the seismograph’s drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum’s vibrations.

- Monitoring Earthquakes

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The First Seismograph?• Designed by the Chinese philosopher Chang Hêng in 132 A.D.• Said to be able to detect earthquakes 400 miles (644 km)

away!

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Methods Used For Earthquake Prediction1. Increase in the rate of a seismic creep and the slow

movement along the fault

2. Gradual tilting of the land near the fault zone

3. Drop or rise in the water level of a well

4. Decrease in the number of micro-quakes and foreshocks

5. Animal behavior

*None of these methods are 100% accurate!

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Instruments That Monitor FaultsIn trying to predict earthquakes, geologists have developed instruments to measure changes in elevation, tilting of the land surface, and ground movements along faults using GPS.

- Monitoring Earthquakes

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Friction• Friction is the force that is exerted on two surfaces

as they rub against one another.• The strength of the friction force depends on two

things:1. How hard the surfaces are pushed together2. What material the surface is made of

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Types of Friction

1. Static friction acts on objects that are at rest.2. Sliding friction occurs when two solid surfaces

slide past one another.3. Rolling friction occurs when an object rolls

across a surface.4. Fluid friction occurs when a solid object moves

through a fluid.

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What type of friction is occuring?

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What type of friction is occurring?

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What type of friction is occurring?

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What type of friction is occurring?

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Gravity• Gravity is a force that pulls objects toward one another.• Gravity keeps objects in place unless they are acted on

by an outside force!• Sir Isaac Newton accurately described this in his law of

universal gravitation.• Gravity acts on all objects regardless of their size and or

location in the universe.• This means that all objects are attracted to one another

but there are some rules involved in how much attraction occurs

• This is mostly due to differences in mass• What is the difference between mass and weight?• Mass is the amount of matter in an object.• Weight is the measure of gravitational force on an object.

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Using Seismographic DataThe map shows the probability of a strong earthquake along the San Andreas fault. A high percent probability means that a quake is more likely to occur.

- Monitoring Earthquakes

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SequencingAs you read, make a flowchart like the one below that shows how a seismograph produces a seismogram. Write each step of the process in a separate box in the order in which it occurs. How a Seismograph Works

Incoming seismic waves

Vibrate the rotating drum

The suspended pen remains motionless and records the drum’s vibration.

- Monitoring Earthquakes

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End of Section:Monitoring

Earthquakes

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Earthquake RiskGeologists can determine earthquake risk by locating where faults are active and where past earthquakes have occurred.

- Earthquake Safety

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How Earthquakes Cause Damage1. Shaking: the shaking caused by seismic waves can trigger

movement of the soil at high elevations and destroy man made structures.

2. Liquefaction: is the result of shaking the soil particles often caused by increased water content and reduces the strength or stiffness of the soil.

3. Aftershocks: are caused by additional releases of energy in rocks after the larger earthquake occurred in the same area.

4. Tsunamis: “harbor waves” result from a large body of water displacement caused by a disturbance in the water.

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How Earthquakes Cause DamageA tsunami spreads out from an earthquake's epicenter and speeds across the ocean.

- Earthquake Safety

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Designing Safer BuildingsTo reduce earthquake damage, new buildings must be made stronger and more flexible.

- Earthquake Safety

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Asking QuestionsBefore you read, preview the red headings and ask a what, how, or where question for each heading. As you read, write answers to your questions.

Where is the quake risk highest? Earthquake risk is the highest along faults and where past earthquakes have occurred.

How do earthquakes cause damage? Earthquake damage occurs as a result of shaking, liquefaction, aftershocks, and tsunamis.

How can you stay safe during an earthquake?

The best way to stay safe during an earthquake is to drop, cover, and hold.

What makes buildings safe from earthquakes?

Buildings can be made safer by being built stronger and with greater flexibility.

- Earthquake Safety

Question Answer

Earthquakes

Earthquake Damage

Click the Video button to watch a movieabout earthquake damage.

- Earthquake Safety

Earthquakes

More on Earthquake Risk

Click the PHSchool.com button for an activity about earthquake risk.

- Earthquake Safety

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End of Section:Earthquake Safety

Earthquakes

Graphic Organizer

faultCompression produces

Effect

Normal fault produces

Cause of Fault

produces fault

Reverse

Tension

Shearing Strike-slip

Earthquakes

End of Section:Graphic Organizer