CHAPTER 4Mrs. Bartley’s Earthquakes

FORCES INSIDE EARTH Objectives

Explain how earthquakes result from the buildup of stress in Earth’s crust

Contrast normal, reverse, and strike-slip faults

CAUSES OF EARTHQUAKES Passing the Elastic Limit Causes

FaultingApplied stresses can cause rocks to bend

and stretch Eventually rocks will break away from one

anotherArea in which the rocks break and

move is called a faultVibrations produced is called an

earthquakeEarth’s crust movement causes the stresses

applied

TENSION The rocks on the crust are being

stretched as two plates are moving apart

The middle becomes thinner until a normal fault occurs

TYPES OF FAULTS P.120 Normal Fault

Earth’s plates move apart

Movement of the plates causes tension

Rocks above the fault surface move downward in relation to the rocks below the fault surface

RIO GRANDE RIFT VALLEY

COMPRESSION This stress force squeezes rock until it

folds or breaks This can create a reverse fault

TYPES OF FAULTS P.121 Reverse Faults

Compression forces are applied because Earth’s plates are coming together

Causes rocks to bend and break

Rocks above the fault surface are forced up and over the rocks below the fault surface

NORTHERN ROCKY MOUNTAINS

SHEARING This stress force pushes rock in two

opposite directions This can cause a strike-slip fault

TYPES OF FAULTS P.121 Strike-slip Fault

Earth’s plates move sideways to one another

Creates a shear force

Rocks on either side of the fault surface are moving past each other without much upward or downward movement

SAN ANDREAS FAULT

EARTHQUAKE INFORMATION Objectives

Compare and contrast primary, secondary, and surface waves

Explain how an earthquake epicenter is located using seismic wave information

Describe how seismic wave studies indicate the structure of Earth’s interior

TYPES OF SEISMIC WAVES P.125 Earthquake focus

Focus – the point in Earth’s interior where the energy waves are produced

Seismic wavesSeismic wave - the energy waves that move

outward from the earthquake focus and make the ground quake

EpicenterThe point on Earth’s surface directly above

the earthquake focus

TYPES OF SEISMIC WAVES P.127 Seismic Waves

Primary wavesEnergy waves that cause rocks to

move back and forth in the same direction

Compression and stretching forces are created

Secondary wavesEnergy waves that cause rocks to

move at right angles to the wave

TYPES OF SEISMIC WAVESSurface waves

Energy waves that reach the Earth’s surface

Energy waves that move rocks in an elliptical motion

LOCATING AN EPICENTER P.130 Seismic waves do not travel through

earth’s surface at the same speedPrimary waves are the fastestSurface waves are the slowest

Seismograph stationsRecord the information from the earthquake

by recording the different types of waves as they reach the station

LOCATING AND EPICENTER P.131 Epicenter Location

If information is received from the earthquake at three stations, then the epicenter can be located

A circle is drawn around each station on a mapThe radius is equal to the distance

from the station to the epicenterThe point in which all three circles intersect

is the earthquake epicenter

USING SEISMIC WAVES TO MAP EARTH’S INTERIOR The speed of the waves changes as the

depth changesThe speed changes in accordance to the

density of the layers of Earth

USING SEISMIC WAVES TO MAP EARTH’S INTERIOR Structure of Earth

Inner coreSolid and very denseComposed of mostly nickel and

ironOuter core

Liquid layer that surrounds the inner core

Composed of nickel and iron

USING SEISMIC WAVES TO MAP EARTH’S INTERIOR

MantleLargest layer located above the

inner coreComposed of silicon, oxygen,

magnesium, and ironCrust

Outermost layerSolid and similar in composition to

the mantle

USING SEISMIC WAVES TO MAP EARTH’S INTERIOR Moho Discontinuity

Boundary between the crust and the mantleSeismic waves speed up as they reach this

area Seismic waves speed up as they

reach more dense areas and slow down when the reach less dense areasThe more solid the layer the more dense

USING SEISMIC WAVES TO MAP EARTH’S INTERIOR Shadow zone

The area between 105-140 degrees from the epicenter

Area in which seismic waves can’t be detected

What is the cause?Secondary waves can’t be

transmitted through liquid layersPrimary waves are slowed and

deflected by the outer core and speed up again when the reach the solid inner core

DESTRUCTION BY EARTHQUAKES Objectives

Define magnitude and Richter scaleList ways to make your classroom and home

more earthquake safe

MEASURING EARTHQUAKES P. 135 Seismology

Seismologists - People who study earthquakes and seismic waves

Use instruments called seismographsRecord seismic wavesA drum with a sheet of paper

vibrates and a stationary pen marks the vibrations on the paper

The height of the lines are used to measure the energy released from the earthquake called the magnitude

MEASURING EARTHQUAKES P.128 Earthquake Magnitude

Usually determines the strength of the break

Doesn’t determine the duration or the sizeFor each increase of 1is 10 times stronger

An earthquake of 4 is 10 times stronger than an earthquake of 3

TSUNAMIS P.137 Caused by the movement of the

ocean floorCauses a disruption in the waterSome are so wide that a large ship can

travel over the wave without knowingRecent earthquake in the Indian Ocean

created a tsunamis that was 100 feet high and moving at 500 mph

EARTHQUAKE SAFETY Quake proofing your home

Place heavy objects near the floorFix gas appliances in place

9.4 LIVING ON A FAULT Objectives

Recognize that most loss of life in an earthquake is caused by the destruction of human-made structures

Consider who should pay for making structures seismic safe

WHO SHOULD PAY FOR EARTHQUAKE PREPARATION? Seismic safe structures

Structures that are resistant to the vibrations of Earth’s crust

Structures are made with mooringsMade of steel and are filled with

alternating layers of rubber and steel

These structures absorb the energy produced from the earthquake