Earthquakes

Types of Seismic Waves

Seismic waves carry energy from an earthquake away from

the focus, through Earth’s interior, and across the surface.

Earthquakes

. *Focus: Point beneath the earth’s surface where

the earth moves

*Epicenter: The point on the surface directly

above the focus. It is where the strength of the

earthquake is strongest.

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Earthquakes

Types of Seismic Waves

P 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

Types of Seismic Waves

Surface waves move more slowly than P waves and S waves,

but they produce the most severe ground movements.

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Earthquakes

Seismic Waves Activity

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fp&wcsuffix=1022&area=view&x=8&y=7ss

- Earthquakes and Seismic Waves

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Earthquakes - Forces in Earth’s Crust

Types of Stress

The stress force called tension pulls on the crust, stretching

rock so that it becomes thinner in the middle.

Earthquakes

Types of Stress

The stress force called compression squeezes rock until it

folds or breaks.

- Forces in Earth’s Crust

Earthquakes

Types of Stress

Stress that pushes a mass of rock in two opposite directions

is called shearing.

- Forces in Earth’s Crust

Earthquakes

Kinds of Faults

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

faults.

- Forces in Earth’s Crust

Earthquakes

Kinds of Faults

A reverse fault has the same structure as a normal fault, but

the blocks move in the opposite direction.

- Forces in Earth’s Crust

Earthquakes

Kinds of Faults

In 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

Changing Earth’s Surface

Over 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

Changing Earth’s Surface

Over 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 Vocabulary

A 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.

Earthquakes

Measuring Earthquakes

The Mercalli scale was developed to rate earthquakes

according to the amount of damage at a given place.

- Earthquakes and Seismic Waves

Earthquakes Richter Scale

The Richter Scale for measures the 'size' or 'strength' of an

earthquake. This scale is quantitative and based on the

amount of energy released by an earthquake.

The energy of a quake is a function of both the amplitude

and the duration of a single wave.

The seismogram below shows waves with a wide range of

amplitude and duration.

This would be magnitude 8 quake!

Earthquakes - Earthquakes and Seismic Waves

Earthquakes

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

Earthquakes

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

Earthquakes

Seismic Wave Speeds

7 minutes

Reading Graphs:

How long did it take the S

waves to travel 2,000 km?

- Earthquakes and Seismic Waves

Earthquakes

Seismic Wave Speeds

4 minutes

Estimating:

How long did it take the P

waves to travel 2,000 km?

- Earthquakes and Seismic Waves

Earthquakes

Seismic Wave Speeds

2,000 = 3.5 minutes

4,000 = 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 Epicenter

Geologists use seismic waves to locate an earthquake’s

epicenter.

- Earthquakes and Seismic Waves

Earthquakes

The Modern Seismograph

Seismic 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

Earthquakes

Instruments That Monitor Faults

In trying to predict earthquakes, geologists have developed

instruments to measure changes in elevation, tilting of the

land surface, and ground movements along faults.

- Monitoring Earthquakes

Earthquakes

Using Seismographic Data

The 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

Earthquakes

Earthquake Risk

Geologists can determine earthquake risk by locating where

faults are active and where past earthquakes have occurred.

- Earthquake Safety

Earthquakes

How Earthquakes Cause Damage

A tsunami spreads out from an earthquake's epicenter and

speeds across the ocean.

- Earthquake Safety

Earthquakes

Designing Safer Buildings

To reduce

earthquake

damage, new

buildings must be

made stronger and

more flexible.

- Earthquake Safety

Earthquakes

Asking Questions

Before 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 - Volcanoes and Plate Tectonics

Volcanoes and Plate Boundaries

Volcanic belts form along the boundaries of Earth’s plates.

Earthquakes

Volcanoes and Plate Boundaries Volcanoes often form where two oceanic plates collide or where an oceanic plate collides with a continental plate. In both situations, an oceanic plate sinks through a trench. Rock above the plate melts to form magma, which then erupts to the surface as lava.

- Volcanoes and Plate Tectonics

Earthquakes

Hot Spot Volcanoes

A volcano forms above a hot spot when magma erupts through the crust and reaches the surface.

- Volcanoes and Plate Tectonics

Earthquakes

Properties of Magma

Magma’s viscosity depends on its physical and

chemical properties.

Magma is made of elements and of

compounds, among them silica.

Viscosity depends on silica content and

temperature.

- Volcanoes and Plate Tectonics

Earthquakes

Magma Composition

Magma varies in

composition and is

classified according

to the amount of

silica it contains.

The graphs show

the average

composition of the

two types of

magma.

- Properties of Magma

Earthquakes

Magma Composition

Silica, other oxides, and other

solids.

Reading Graphs:

Study both graphs. What

materials make up both types

of magma?

- Properties of Magma

Earthquakes

Magma Composition

Rhyolite-forming magma;

about 70 percent.

Reading Graphs:

Which type of magma has

more silica? About how much

silica does this type of

magma contain?

- Properties of Magma

Earthquakes

Magma Composition

About 60 percent

Estimating:

A third type of magma has a silica content that is halfway between that of the other two types. About how much silica does this type of magma contain?

- Properties of Magma

Earthquakes

Magma Composition

Rhyolite-forming magma

would have higher viscosity

because it is higher in

silica.

Predicting:

What type of magma would have a higher viscosity? Explain.

- Properties of Magma

Earthquakes

Magma Reaches Earth’s Surface

When a volcano erupts,

the force of the expanding

gases pushes magma from

the magma chamber

through the pipe until it

flows or explodes out of

the vent.

- Volcanic Eruptions

Earthquakes

Composite Volcano Eruption Activity

Click the Active Art button to open a browser window and

access Active Art about composite volcano eruption.

- Volcanic Eruptions

Earthquakes

Kinds of Volcanic Eruptions

Within the last 150 years, major volcanic eruptions have

greatly affected the land and people around them.

- Volcanic Eruptions

Earthquakes

Landforms From Lava and Ash

Volcanic eruptions create landforms made of lava, ash, and

other materials. These landforms include composite

volcanoes, shield volcanoes, cinder cone volcanoes, and

lava plateaus.

- Volcanic Landforms

Earthquakes

Landforms From Lava and Ash

A caldera forms when an

volcano’s magma chamber

empties and the roof of the

chamber collapses. The

result is a large, bowl-

shaped caldera.

- Volcanic Landforms

Earthquakes

Landforms From Magma

Features formed by magma include volcanic necks, dikes,

and sills, as well as batholiths and dome mountains.

- Volcanic Landforms

Earthquakes

Batholiths

A batholith is a mass of rock formed

when a large body of magma cools

inside the crust. Several large batholiths

form the core of mountain ranges in

western North America. Half Dome in

Yosemite National Park, California, is

part of the Sierra Nevada batholith.

- Volcanic Landforms

Earthquakes

Outlining

As you read, make an outline

about volcanic landforms that

you can use for review. Use

the red headings for the main

topics and the blue headings

for the subtopics.

Volcanic Landforms

I. Landforms From Lava and Ash

A. Shield Volcanoes

B. Cinder Cone Volcanoes

C. Composite Volcanoes

D. Lava Plateaus

E. Calderas

F. Soils From Lava and Ash

II. Landforms From Magma

A. Volcanic Necks, Dikes and

Sills

B. Dikes and Sills

C. Batholiths

D. Dome Mountains

III. Geothermal Activity

A. Hot Springs

B. Geysers

C. Geothermic Energy

- Volcanic Landforms