I INVITE YOU TO KNOW THE EARTH II - PreventionWeb

THE EARTH II

TO KNOW

I INVITE YOU

5th to 8th GRADE

SERVICIO HIDROGRAFICO Y OCEANOGRAFICO DE LA ARMADA DE CHILEC O M M I S S I O N

I C E N T E RI N T E R G O V E R N M E N TA L O C E A N O G R A P H I C

N T E R N A T I O N A L T S U N A M I I N F O R M A T I O N

OF PREPARATORY SCHOOLTEXTBOOK

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I INVITE YOU TO KNOW THE EARTH II

5th to 8th Grade of Preparatory School

ABOUT THE TEXTBOOK

AUTHORS

EDITORIAL ASSISTANCE

REVIEWERS

This book is the result of both the implementation ofRecommendation ITSU-Xl11.3 of the Thirteenth Session ofthe International Co-ordination Group for the TsunamiWarning System in the Pacific, and the work of severaleducation experts. An ad-hoc Working Group headed by H.Gorziglia (Chile), revised the work done by the experts whowere partially funded by the IntergovernmentalOceanographic Commission.

Margot Recabarren**, Education ExpertYarimy Arcos**, Preparatory School TeacherEmilio Lorca***, Geologist

Leopoldo Toro***, DesignerHumberto Bahamondes***, Illustrator

Hugo Gorziglia***, DirectorElvira Arriagada*, Risk Prevention Expert

(*) Secretaría Ministerial de Educación, Va. Región, Chile(**) Dirección de Educación de la Armada, Chile(***) Servicio Hidrográfico y Oceanográfico de la Armada, Chile

CONTENTS

UNIT I

UNIT II

UNIT IV

UNIT V

THE OUTSIDE OF THE EARTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

1.- What is the shape of the earth? What are its dimensions? . . . . . . . . . . . . . . . . . . . 52.- How much water is there on the earth? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.- What does the bottom of the ocean look like? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

THE INTERIOR OF THE EARTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-111.- Could we know the inside of the earth? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.- Let's learn about the interior of the earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.- And the origin of the continents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.- What is plate tectonics? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195,- What are plate boundaries? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

UNIT Ill

EARTHQUAKES AND VOLCANOES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-231.- How are volcanoes born? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.- What are earthquakes and how are they produced? . . . . . . . . . . . . . . . . . . . . . . . 273.- How are earthquakes measured? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294.- Can earthquakes be forecast? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

TSUNAMIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-331.- Let's learn about tsunamis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352.- Tsunami propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373- Tsunami origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394.- Coastal effects of a tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

TSUNAMI PROTECTION MEASURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-431.- How should we protect ourselves from tsunamis? . . . . . . . . . . . . . . . . . . . . . . . . . 452.- If you are at home or at school . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

I INVITE YOU TO KNOW THE EARTH II 1


I AM TOMMY TSUMI

YOUR GUIDE AND FRIEND

IN THIS EXPLORATION.

WELCOME

TO THIS

ADVENTURE

I INVITE YOU TO KNOW THE EARTH II2

UNIT I

3

THE SURFACE

OF THE EARTH


4

Polar flattening

Equatorial bulking

The earth is fatty

DRAWING 2

DRAWING 1

MEASURES OF THE EARTH

EQUATOR

POLES

DIAMETER RADIUS

Equatorialdiameter12.756 Km

Polar d12.713 Kms

iameter

Equatorial radius

Polar radius


5

WHAT IS THE SHAPE OF THE EARTH?

As we know, the earth is just one of the millions ofbodies in the Universe. However, the earth is notjust a planet, but one of the few, or maybe theonly one having the natural conditions allowingthe existence ot plant and animal life, andtherefore of Man. The earth has the shape of asphere slightly flattened at the poles. Do youknow how this can be shown? Let's start bycomparing the different dimensions of the earth.

WHAT ARE ITS DIMENSIONS?

The earth's shape is an oblate spheroid, flattenedat the poles. To a first approximation the earth isan ellipsoid of revolution (spheroid). Itsdimensions are: equatorial radius = 6,378kilometers; polar radius = 6,356 kilometers;circumference = 40,000 kilometers. Also comparethe measures of radii and diameters in drawing 2.Enter the values in the table.

Look carefully at the drawings on each page andperform the activities proposed by Tommy Tsumi.

ACTIVITY:

Locate in thedrawing of the earththe measurementscorrespondingto the polarand equatorialradii.

Compare them.

Which is larger?

THE EARTH IS FLATTENED AT THE POLESAND THIS CAN BE SHOWN BECAUSE THE

EQUATORIAL RADIUS AND DIAMETER ARELARGER THAN THE POLAR RADIUS AND

DIAMETER.


6

SO MUCH WATER!The Pacific ocean

is the biggest.

The Indianocean is warmer!How wonderful

is the water

Tha Atlantic oceanis the most traveled!Bye, bye, I’m going

to Europe.

DRAWING 2

DRAWING 1

Oceans and continents.


South Atlantic OceanSouth Pacific Ocean

North Pacific Ocean

North Atlantic Ocean

Indian Ocean

Arctic Ocean Arctic OceanArctic Ocean

North Pacific Ocean

United States of America

U.S.A.

Canada

Mexico

Brazil

U. S. A.

French Polynesia (Fr.)

ArgentinaUruguay

Paraguay

Chile

Bolivia

Peru

Ecuador

Colombia

VenezuelaFrench Guiana (Fr.)

SurinameGuyana

The Bahamas

CubaDominican Republic

PanamaCosta Rica

Nicaragua

HondurasGuatemala

El Salvador

Trinidad and Tobago

Jam.Haiti Puerto Rico (US)

Greenland (Den.)

Iceland

Madagascar

South AfricaLesotho

Swaziland

Mozambique

Tanzania

BotswanaNamibia Zimbabwe

Angola

Zaire

Zambia

Malawi

Burundi

KenyaRwanda

Uganda

Congo

Gabon

Somalia

Ethiopia

Sudan

Djibouti

Belize

EgyptLibya

Chad

Niger

Algeria

Mali

Tunisia

Nigeria

CameroonC. A. R.

Benin

TogoGhana

Burkina FasoBarbados

Dominica

Côte D’Ivoire

Liberia

Sierra Leone

GuineaGuinea-Bissau

SenegalThe Gambia

Mauritania

Western Sahara (Mor.)

Morocco

Finland

Norway

Sweden EstoniaLatvia

Lithuania

Poland

Romania

Bulgaria

TurkeyGreece

Czech.

Hung.

ItalyAlbania

Portugal

France

Spain

Aus.Switz.

United Kingdom

Ireland

Den.

GermanyNeth.

Bel.

Cyp.

Yemen

OmanSaudi ArabiaU. A. E.

Qatar

IranIraq

Syria

Jordan

IsraelLeb. China

Mongolia

Russia

Afghanistan

Pakistan

India

Sri LankaMaldives

NepalBhu.

Myanmar (Burma)Bang.

Andaman Islands (India)

Thailand

Indonesia

Malaysia

Brunei

Philippines

Taiwan

Cambodia

Vietnam

Laos

Australia

Papua New Guinea

New Zealand

Fiji

New Caledonia

Solomon Islands

Kiribati

Marshall IslandsFederated States of Micronesia

Guam (USA)

Japan

N. Korea

S. Korea

Kuril Islands

Wrangel Island

Aleutian Islands (USA)

New Siberian Islands

Severnaya Zemlya

Novaya Zemlya

Franz Josef LandSvalbard (Nor.)

Jan Mayen (Nor.)Banks Island

Victoria Island Baffin Island

Ellesmere Island

Island of Newfoundland

Antarctica

Îles Crozet (France)

Tasmania

South Georgia (adm. by UK, claimed by Argentina)

Falkland Islands (Islas Malvinas) (adm. by UK, claimed by Argentina)

KuwaitCanary Islands (Sp.)

Sao Tome & Principe

SingaporeEq. Guinea

Faroe Is. (Den.)

Kazakhstan

Belarus

Ukraine

Moldova

GeorgiaArmenia Azerbaijan

Turkmenistan

UzbekistanKyrgyzstan

Yugo.

Mac.

Slov.Cro.

Bos.

Slovak.

Eritrea

Tajikistan

Hawaiian Islands

Galapagos Islands (Ecuador)

Mauritius

Seychelles

120° 60° 0° 60° 120° 180°

60°

30°

0°

30°

60°

180°150°120°90°30°0°30°60°90°120°150°

60°

30°

0°

30°

60°

60°

Robinson ProjectionI994 MAGELLAN GeographixSMSanta Barbara, CA (800) 929-4MAP

7

DO YOUKNOW?

The Pacific Oceanis so largethat al thecontinents puttogether couldfit into it.It covers165,200,000squarekilometers.

ACTIVITY:

Write thename ofeveryocean youknow indrawing 1.

OCEAN COVER ¾ OF THEEARTH’S SURFACE, THE

PACIFIC OCEAN BEING THELARGEST AND DEEPEST OF ALL.

One of the most relevant aspects of its surface isthe vast expanse of the oceans. More than 70 % ofthe surface of our planet is covered by oceans andin the Southern Hemisphere the oceans representalmost 85 % of the total surface, as seen indrawing 1.

The Pacific Ocean is the largest ocean on theearth, encompassing more than one third of thetotal surface of the planet. It is also the deepestocean. Its mean depth is 200 meters greater thanthe oceanic average of 3,700 meters. It is in thePacific Ocean, because of its size and thegeological structure of its ocean floor, where mostof earthquakes and tsunamis of the world occur.

The Pacific Ocean is surrounded mainly by linearmountain chains, trenches, and island arc systems.Locate them in drawing 2 ... as ou can see theocean bottom is not flat. Its landscape is asinteresting and varied as the one you see on thesurface of the earth.

HOW MUCH WATER IS THERE ON THE EARTH?


8

DEEPEST PLACE

CONTINENTALRIDGE

SHORT DISTANCE

HIGHESTMOUNTAIN

OCEANIC TRENCH

DRAWING1

DRAWING 2

Bottom of the Pacific Ocean.

LIST OF TRENCH AND RIDGES:

1.2.3.4.5.6.7.8.9.

10.11.12.13.14.


9

ACTIVITY:

Mark ondrawing 1,the trenchand theridge.

THE BOTTOM OF THE OCEANSHOWS RIDGES IN THE MIDDLEOF THE OCEANS (MID-OCEANIC)AND MARINE TRENCHES CLOSETO THE CONTINENTS.

WHAT DOES THE BOTTOMOF THE

OCEAN LOOK LIKE?

If all the water was removed from the oceanbasins, there would be revealed a system ofridges and rises encircling the globe withintervening deep-sea basins between theridges and the continents. As you can see indrawing 1, the deepest parts of the oceans areclose to the continental boundaries, they arecalled MARINE TRENCHES.

The oceans are not as deep near their centersdue to the presence of MID-OCEANICRIDGES ("mid" means it is in the middle).

Almost ever continental ridge is near acontinental boundary and in front of a deepocean trench. Thus, continents and oceansshow the greatest difference in elevation oververy short distances, as can be seen indrawings 1 and 2.


10

UNIT II


11

THE INTERIOR

OF THE EARTH


12

RECORDINGPAPER

REVOLVINGDRUM

SPRING

HEAVYWEIGHT

PEN

BEDROCK

Seismograph

Seismograph and seismogram.

P-Wave S-Wave

Surface waves1 min


13

DO YOU KNOW?

Every year, ten ormore bigearthquakes shakeour planet.The smallest ofthese eartquakesreleases energyequivalent to onethousand timesthe energyreleased by anatomic bomb.

ACTIVITY:

With yourclass, visit aninstitution thathas seismicinstrumentand observetheseinstrumentsin operation.

The internal structure of the earth hasbeen determined thanks to seismology.Seismic waves cross the different layersof the earth. There are 3 types of waves:

P or primary waves, S or secondarywaves, and surface waves.

Nobody can make a trip to the center of our planetto discover its internal structure, that is, thematerial it is made of. However, today we knowthe internal structure thanks to instruments thatrecord the waves produced by earthquakes.

Seismic waves go through the different layers ofthe earth and we can learn the characteristics ofthe areas they cross by their propagationvelocities.

Whenever a fault is activated, three types ofseismic waves are produced: P wavescorresponding to primary or longitudinal waves, Sor secondary waves, and surface waves.

These waves are recorded using an instrumentcalled a seismograph, through which we candetermine the magnitude and location of theearthquake.

Until the beginning of seismology, our knowledgeabout the interior of the earth was based onhypothesis and speculation. Today, thanks to thisscience, we know a lot about the structure of theearth.

COULD WE KNOW THE INTERIOR OF THE EARTH?


14

CRUST

MANTLE

OUTERCORE

INNERCORE

Layers of the earth.


15

DO YOU KNOW?

Pressure at theborder betweenthe inner and theouter core is 3.3millionatmospheres.

That isequivalent to thepressure of a pileof 3,300 mediumsize car on thesurface of afingernail.

LET’S LEARN ABOUT THE INTERIOR OF THE EARTH...

REVIEW:

The earth is divided into three layers:Crust (continental and oceanic crust),Mantle (upper and lower mantle) andCore (outer and inner core).

The interior of the earth is made of layers withdifferent characteristics. These layers are classifiedin different ways. We are going to learn only oneof this classifications at the moment.

We will divide the earth into three basic layers:

, is the layer covering the earth's ground. Itis composed of solid rock and has more rigiditythan the next layer. its thickness varies between 5and 60 kilometers and averages 33 kilometers. Thecontinental crust is where we live, and the oceaniccrust covers the bottom of the oceans.

, this layer is under the crust and goesdown to a depth of 2,900 kilometers. It is dividedinto two regions: the upper mantle from the baseof the crust to a depth of 700 kilometers, and thelower mantle from that point down to the surfaceof the core.

, composed of the liquid outer core locatedbetween depths of 2,880 and 5,000 kilometers,and the inner core that is solid and has a radius of1,200 kilometers.

Although the crust and the mantle are composedby several kinds of rocks, the inner core is mademainly of iron and nickel.

CRUST

MANTLE

CORE


16

200 million years ago



In another 50 million years

To day

Formation and Breakup of Pangea.

Trilobite (200 million year fosils).


17

DO YOUKNOW...?

“CONTINENTALDRIFT”.

theory isknown asthe theory of

Wegener’s

ACTIVITY:

Find out...What othertype offossils canbe found inthe rocksof themountains?

Alfred Wegener established that at thebeginning there was just one continent thatsplit apart to start the origin of thecontinents you know. They drifted slowly totheir present positions, and are still drifting:this is the theory of Continental Drift.

Many mysteries about our planet have stirred thecuriosity of observant people. Earlier in thiscentury, explorers were amazed to find rocks withfossil imprints of ferns in the frozen lands of theArctic and the Antarctic. How could plants thatthrive in warm, moist climates exist in what is nowa harsh climate? What changes had taken place?

In 1912, Alfred WEGENER, a German scientistproposed a theory that all the continents wherejoined in the past in a huge megacontinent called"PANGAEA”, which means "every lands" in Greek.

Wegener believed that Pangaea began breaking upand drifting a art many millions of ears ago. Heinsisted that C jigsaw puzzle fit Y1the continentswas not an accident, but the result of the splittingof Pangaea. He said that the continents slowlydrifted over the ocean floor until they reachedtheir present positions.

If you look at the shape of the eastern coastline ofSouth America you will see that it fits very wellwith Africa, as if they were joined sometime in thepast. Although Wegener's theory is not completelycorrect, it allowed scientist to understand that theearth's crust is not static, and to make otherimportant discoveries.

... AND THE ORIGIN OF THE CONTINENTS?


0

Kilometers

5000

Euroasian Plate

PhilippinePlate Cocos

Plate

CaribbeanPlate

Eurasian Plate

ArabianPlate

AfricanPlate

AntarcticPlate

18

Plate boundaries map.

LOCATE!

5

1

43

2

3


Scientific discoveries in the 1960's and Wegener'stheory of continental drift suggested that theAtlantic Ocean was growing. Can an ocean grow?Is the earth's crust moving? Answer these questionafter reading the text.

In this map you can see the earth is divided intoabout 20 big sections called "plates". These plateshave an average thickness of 70 kilometers. Themap shows that a plate can contain bothcontinental and oceanic crusts.

Plates can spread, collide or slide with each other.Arrows in the map show present direction ofmovement of each plate. Probably in the past thedirections of movement were different.

The region where plates come in contact witheach other is call a "plate boundary ". The wayone plate moves with respect to another onedetermines what happens in their boundary.

After this answer the questions.

Could oceans grow?

Is the crust of the earth moving?

19

DO YOUKNOW...?

Plates move atspeeds of up to15 centimetersper year atmost.The plate withthe greatestvelocity is thePacific plate.

ACTIVITY:

Find out thenames ofthe platesnumber 1,2, 3, 4 and 5on the map.

WHAT IS PLATE TECTONICS?

OVERVIEW

The earth is divided into about 20 hugeplates, each of which can contain bothcontinental and oceanic crust. The placewhere plates meet is called a “PlateBoundary”.

YES NO


20

Ridge

TrenchPlate Magma

Spreading boundary

Colliding boundary

Fault boundary

Plate

Plate

DRAWING 1

DRAWING 2

DRAWING 3

Displacement of the tectonics plates.

Plate boundaries.

0

Kilometers

5000

North AmericanPlate

Euroasian Plate

Pacific Plate

PhilippinePlate

Australian-IndianPlate

CocosPlate

CaribbeanPlate

Eurasian Plate

ArabianPlate

AfricanPlate

AntarcticPlate

Australian-IndianPlate

NazcaPlate

SouthAmerican

Plate


21

DO YOU KNOW?

Iceland, andisland in thenorth Atlantic,emerged fromthe spreadingin theMid-AtlanticRidge.

ACTIVITY:

Look carefully atthe tectonic platesmap and mark withcolored pencils thedifferent plateboundaries.Mark them asfollows:Collidingboundaries=Spreading

=Fault

=

boundaries

boundaries

red

green

blue

WHAT ARE PLATE BOUNDARIES?

There are three types of plate boundaries:spreading boundaries forming mid-oceanicridges, colliding boundaries where platesbump into each other and fault boundarieswhere plates rub past each other.

SPREADING BOUNDARIES

COLLIDING BOUNDARIES

SLIDING BOUNDARIES

are found whereplates are moving apart at mid-ocean ridges(drawing 1). New crust forms at spreadingboundaries. Volcanoes steam and the earthtrembles with great regularity along this mid-oceanridge. When Pangaea broke, it separated along theMid-Atlantic Ridge. It took 200 million years forthe Atlantic to grow to its present size.

form where twoplates bump into each other. The leading edge ofone plate sinks into the mantle under the edge ofanother plate (drawing 2). Trenches bordering thePacific Ocean are regions where the Pacific plateis sinking ... this is why this ocean is slowlyshrinking.

occur where two platesrub past each other (drawing 3).


22

UNIT III


23

EARTHQUAKES

AND

VOLCANOES


24

Ash and gases

Crater

Cone

Magma

How volcanoes are born.

CINDER CONE:Forms when eruptions throw outmostly rocks and ash but verylittle lava.

COMPOSITE CONE:Originates with alternatingeruptions of dust, ash, and rockfollowed by quiet lava flows.

SHIELD CONE:Created by non-explosiveeruptions with easyflowing lava.

VOLCANIC DOME:Results from violenteruptions of lava so thickthat it barely flows.


25

DO YOU KNOW?

MAGMA ismolten rock ofvery hightemperaturewhich is in theinterior of theearth. Whenmagma flows tothe exteriorthrough volcanoesit is called LAVA.

REVIEW

Volcanoes can originate at either oceanic orcontinental crust and vary both in their appearanceand material they throw away. They can quietlyooze lava or explode under the pressure of gas andwater vapor within the magma. Earthquakes maysignal the rise of magma inside the volcano.

HOW ARE VOLCANOES BORN?

As we already know volcanoes are openings of theearth's crust that could originate at the oceanic crustby sinking under another oceanic plate, giving rise tovolcanoes in islands that are called island arcs as theJapanese Islands. Volcanoes can also form on thecontinents where an oceanic plate is sinking under acontinental plate, as in South America. Volcanoesdiffer in appearance and behavior. Some volcanoesshoot water vapor and other gases, dust, ash, androcks explosively.

Visualize the effects of shaking a warm soda pop. Thebottle may explode, releasing the soda and carbondioxide, the dissolved gas in the soda. Cases andwater vapor, which are under pressure inside a

volcano, may also explode. One of the biggest volcanic explosions that evertook place was the eruption of the volcano Krakatau, a volcanic island inthe strait between Java and Sumatra. In 1883 it exploded so violently thatpeople heard the explosion 3,200 kilometers away. Most of the islanddisappeared. Volcanic dust remained in the air around the world for twoyears. A giant sea wave created by the explosion killed more than 36,000people on nearby islands.

Volcanoes often give warnings before they erupt. These warnings includegas and smoke from the volcano. Earthquakes may signal the rise of magmainside the volcano. The ground around or on the volcano may bulge or tiltslightly.

If a volcano has erupted in the recent past, it is called an active volcano. Adormant volcano is one that erupted in the past but has been quiet for manyyears. An extinct volcano is one that is not expected to erupt again. Most ofthe volcanoes in the Hawaiian Islands are extinct.


26

A

B

Seismic waves are generatedby the break of the rocks.

Focus of an earthquake.

DRAWING 3

DRAWING 1

EPICENTER

FAULT

SEISMICWAVES

FOCUS

DRAWING 2

Areas of high seismicity.

Pacific Ringof Fire

Mid-AtlanticRidge

MediterraneanBelt


27

ACTIVITY:

Compare the map(drawing 3) withthe plate tectonicsmaps of page 18and 20.Can you explainwhy there is azone called the“Ring of Fire ofthe Pacific”?Discuss this withyour classmates.

An earthquake can be originated by volcanicactivity, however, most of them are producedby movements of rocks along a fault or at aplate boundary. The FOCUS is the point wherethe seismic waves originated at first in theinterior of the earth. The same point projectedonto surface is called the EPICENTER.

WHAT ARE THE EARTHQUAKESAND HOW ARE THEY PRODUCED?

An earthquake is a trembling or shaking of theearth. A big earthquake is one of the strongestforces of nature and it produces large scaledestruction.

Someearthquakes are caused by volcanic activity.During a volcanic eruption, magma ascendingthrough the volcano's interior shakes the crustproducing an earthquake. However, most of theearthquakes are produced by the movement ofrocks along a fault and by the energy released atplate boundaries.

rocks have a certain amount ofelasticity and when they are under pressure theyfold, but if the pressure is very high they finallybrake and go back to their original position. AFAULT is a brake in the earth's rocks along whichthe two sides have been displaced relative to eachother. When a brake occurs a big amount ofenergy is released as SEISMIC WAVES, as seen indrawing 2. The place where the earthquakeoriginated is called the FOCUS or HYPOCENTER,and the place on the surface of the earth locatedover the focus is called the EPICENTER.

With highly sensitive seismographs installedaround the world, it's easy to record seismicevents, even if they are not felt by man. Once theseismic waves have been detected and recorded atseveral seismic stations, it is possible to determinethe place where they have come from and thetime they were produced.

HOW ARE THEY ORIGINATED?

See drawing 1:


28

MODIFIED MERCALLI INTENSITY SCALE

I Not felt except by a very few persons under especially favorablecircumstances.

II Felt only by a few persons at rest, especially on upper floors of buildings.

III Felt quite noticeable indoors, especially on upper floors of buildings, butmany people do not recognize it as an earthquake.

IV During the day, felt indoors by many people. Dishes, windows and doors,disturbed; walls make cracking sound; liquids in open vessels disturbed.

V Felt by nearly everyone. Some dishes, windows, etc., broken. Unstableobjects overturned.

VI Felt by everyone. Some heavy furniture moved. A few instances of fallenplaster or damaged chimneys.

VII Everyone frightened. Overturned furniture in many instances. Trees andbushes shaken strongly. Noticed by persons driving cars. Cornices,brickwork, tiles and stones dislodged.

VIII Damage slight in specially designed structures. Great in poorly builtstructures. Chimneys, factory stacks, columns, monuments and wallscollapse.

IX Every building damaged and partially collapsed. Ground crackedconspicuously. Underground pipes broken. Several landslides reported.

X Some well-built wooden structures destroyed. Most masonry and framestructures destroyed along with their foundations.

XI Few, if any structures remain standing. Bridges destroyed. Damage great todams, dikes, and embankments. Rails bent greatly.

XII Almost everything is destroyed. Objects are thrown into the air. Theground moves in waves or ripples. Large amounts of rocks may move.


29

DO YOU KNOW?

The strongestrecordedearthquakes inhistory occurredin 1960 off coastof southern Chile,and in 1964 off thecoast of Alaska.Both hadmagnitudes over9.1 in the Richterscale.

SUMMARY:

Earthquakes are measured using theintensity (Modified Mercalli) andmagnitude(Richter) scales.

HOW ARE EARTHQUAKES MEASURED?

To measure an earthquake, two scales are used todetermine its intensity and magnitude. Theintensity of an earthquake is the violence withwhich the earthquake is felt at different locationsin the affected area. Its value is determined byassessing the damage produced, the effect onobjects, buildings and grounds, and the impact onpeople.

The intensity value of an earthquake is determinedaccording to a previously established intensityscale, which is different for different countries. Inseveral countries of America it is determined usingthe Modified Mercalli Intensity Scale, graded in 12levels.

The magnitude of an earthquake is the energyreleased at the focus of the earthquake. It ismeasured with the help of an instrument calledseismograph. The instrument's reading (amplitudeof seismic waves) indicates the amount of energyreleased by an earthquake. The greater the waveamplitude, the greater the magnitude. A magnitudescale was devised by the American seismologistCharles Richter in 1935. It uses Arabic numerals.Richter's scale is open-ended; that is, there is noupper or lower limit to Richter magnitudes. Eachwhole-number increase in the magnitude of anearthquake represents about a thirty-fold increasein the amount of energy released.


30

EARTHQUAKE WARNING SIGNS

Warning Sign Detected by

Foreshocks - a series of small tremors. Seismograph

Local variations in the earth's magnetic Magnetometerfield due to changes in rock under pressure. (measures magnetism)

Tilting of the earth's surface due to Tiltmeter (detects tilt)movements caused by a buildup of stress.

Increased levels of radon, Scintillation Countera radioactive gas, in deep wells. (detects radioactivity)Gas is released into the water by rocksunder pressure.

Movement along a fault. Creepmeter - a wireor rod stretched across fault

Rising or failing of the land. Gravity meter

Expansion or contraction of rocks. Strainmeter

Changes in the ability of rocks to Resistivity gaugeconduct electricity.

Changes in the level, temperature, Direct observation,and murkiness of water in wells, thermometersespecially deep wells.

Spreading apart of land along a fault. Laser Range - measuresround-trip travel time of alight beam bounced across afault.

TO DRAW OR STICK (Page 49)


31

ACTIVITY:

Draw or stickdrawings ofthree of theinstrumentsnamed onpage 30.

CAN EARTHQUAKES BE FORECAST?

Presently, scientists are able to recognizesome premonitory “signs” of earthquakes...Someday they will be able to forecastearthquakes without fail.

Where and when will the next earthquake occur? How strong will it be?Scientists are trying to answer these questions.

People all over the world who watch faults find that certain "signs" often occurbefore earthquakes. The ground sometime bulges or tilts near a fault before anearthquake. An increasing number of small earthquakes on a fault could meanthat a strong earthquake is coming. Also, change in the water level in a wellnear a fault is often an earthquake sign. These changes might last for severalmonths before smaller destructive earthquakes or for years before large ones.

Using these signs and many others, scientists have been able to correctly predictsome destructive earthquakes. Perhaps in your lifetime earthquake forecasts willbecome accurate enough to save lives.

A government agency in China has reported thatstrange animal behaviors were observed just hoursbefore an earthquake. Cattle, sheep, mules, andhorses would not enter corrals. Rats fled theirhomes. Hibernating snakes left their burrows early.Pigeons flew continuously and did not return totheir nests. Rabbits raised their ears, jumped aboutaimlessly, and bumped into things. Fish jumpedabove water surfaces.

China was not the only country to report suchunusual animal behavior. Late on May 6, 1976, anearthquake shook a town in Italy. Before theearthquake, pet birds flapped their wings andshrieked. Mice and rats ran in circles. Dogs barkedand howled. Perhaps the animals sensed thecoming earthquake?

DO YOU KNOW ANIMALS CAN PREDICTEARTHQUAKES?


32

UNIT IV


33

TSUNAMIS


34

Earthquake focus

Origin and propagation of a tsunami.


35

ACTIVITY:

Find outwhat countrieshave suffereddestructivetsunamis in thelast 50 years.

LET’S LEARN ABOUT TSUNAMIS

DO YOU KNOW?

In 1883 a seriesof volcaniceruptions inKrakatau(Indonesia)produced apowerfultsunami withwaves as highas a 12 storybuilding.

SUMMARY:A tsunami is a natural disaster occurring after alarge earthquake. It is a series of long wavesmoving at great speed over the ocean. At thecoast they can be as high as 30 meters, causingdamage to cities and people.

The word tsunami is of Japanese origin. If webreak the word in half we see that "tsu" meansharbor and "nami' means wave.

A tsunami is a series of sea waves spreadingrapidly in all directions from the area on the seabottom where a large earthquake, volcaniceruption, or coastal landslide has occurred.

As a tsunami reaches the coast, the first thing thatmay happen is a withdrawal of water. More shoremay be exposed than even at the lowest tides. Thismajor withdrawal of sea water should be taken asa warning of the tsunami wave that will follow. Noone would want to try to outrun a fast-moving ten-meter wave that could smash the shore with greatimpact.

Another tsunamis begin with a rise of the sea level.As the tsunami wave of the maximum heightappears as 2nd. or 3rd. wave, you should not thinkto be safe just after the first tsunami wave attack.

Most tsunamis occur after a large earthquakeunder the ocean, and are due to changes in thesea bottom at faults or plate boundaries.

HOW IS A TSUNAMI CREATED?


36

CANADACHINA

JAPAN

AUSTRALIA

NEWZELAND

TAHITI

HAWAII

UNITEDSTATES

SOUTHAMERICA

PACIFIC OCEAN

60ºN

60ºS90º120º120ºE 150º180º150º 60ºW

30º

30º

0º

Propagation of the tsunami waves fron the Chilean 1960 earthquake.

TAIWANPHILIPPINES


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ACTIVITY:

Find out thelatitude andlongitude ofChile andJapan.Relate themto thedrawing.

SUMMARY:When a tsunami occurs, waves traveling atgreat speed, which can travel great distancesthrough the oceans, change their course due to:

• sphericity of the earth• depth differences in the ocean• marine currents moving obliquely• costal features

TSUNAMI PROPAGATION

The return of sea level to its normal positiongenerates a series of waves propagating in alldirections. These waves are not uniform. They canbe modified by different phenomena:

When a tsunami travels a long distance across theocean, the sphericity of the Earth must beconsidered to determine the effects of the tsunamion a distant shoreline. Waves that diverge neartheir source may converge again at a point on theopposite side of the ocean.

In the drawing you can see a clear example of this,where a tsunami produced in Chile affected theJapanese coast, producing much damage andmany victims.

Tsunami waves can also change direction(refraction of water waves) due to shoaling, as wellas due to oceanic currents moving obliquely to thetsunami direction of propagation.

As a tsunami approaches a coastline, the wavesare modified by the various offshore and coastalfeatures. Submerged ridges and reefs, continentalshelves, headlands, bays of various shapes, andthe steepness of the beach slopes may modify theperiod and height of the tsunami wave .


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39

DO YOUKNOW?

A tsunami is ableto travel throughan entire oceanwith a velocityof up to 900kilometersper hour.

ACTIVITY:

Ask your familyif they rememberany tsunamithat have ocurredin the country.Discuss withyour teacherand classmates.

TSUNAMI ORIGIN

SUMMARY:Tsunamis are local when their effects areproduced inmediately after the occurrence ofthe erthquake; they are distant when theireffects are produced hours after theearthquake’s occurrence in a very distantlocation.

In a local tsunami, the source phenomenon (largeearthquake, submarine volcanic eruption, orcoastal landslide) is very close to the observer.

In this case, the tsunami effects are present almostimmediately after the source phenomenon (largeearthquake, etc.) is over. Lapses of time as short as2 minutes have been observed between theoccurrence of an earthquake and the arrival of thefirst tsunami wave to the nearest coast.

Because of this, a tsunami warning system isuseless in this type of event and we should notexpect instructions from an established system toreact and keep us safe from the possible tsunamiimpact. This operational incapability of thewarning systems is further increased by thepossible communications and systems collapsegenerated by the earthquake. Hence, it isnecessary to have prepared a proper response planin case of a tsunami.

With a distant tsunami, the earthquake or volcaniceruption occurs in one place, and the tsunami isregistered at a different and distant place (severalthousands kilometers away) several hours later.


40

4000m

213Km 23Km

50m

10.6Km

10m

Deep Velocity Wave length(metros) (km/h) (km)

7000 942,9 282

4000 712,7 213

2000 504,2 151

200 159,0 47,7

50 79,0 23,0

10 35,6 10,6

Propagation and changes of tsunami waves near of the coast.


41

DO YOUKNOW... ?

The destructioncaused bytsunamis stemsmainly fromthe impact ofthe waves, theerosion offoundations ofbuildings,bridges androads.

COASTAL EFFECTS OF A TSUNAMI

SUMMARY:Effects produced by a tsunami on thecoast depend on the shape of the seabottom and the coastline, as well as theorientation of the incoming tsunamiwaves.

Effects produced by a tsunami at the coast arevaried. They depend on the shape of the seabottom and the shore, as well as on the tsunamiwave's orientation when arriving at the coastline.As we can see in the drawing, if the sea is deep atthe coast, the rise of the water level will be lessviolent than at a shallow coast.

When a tsunami reaches the coast, the water levelcan rise several meters. In extreme cases, waterlevels have risen 30 meters, however, 10 meters ismore common. This is called tsunami runup, andit can vary greatly from place to place.

An example of how extreme this variation can beis given by some scientists for Haena, on theisland of Kauai, Hawaii, where there was a gentlerise of water level on the western side of the bay,but less than one mile to the east, waves rushed onshore, flattening groves of trees and destroyinghouses.

It should be noted that the characteristics of thewaves may vary from one wave to another at thesame coastal point. Some scientists cite a case inHawaii where the first waves came in so gentlythat a man was able to wade through chest-highwater ahead of the rising water. Later waves wereso violent that they destroyed houses and left aline of debris against trees 150 meters inland.


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UNIT V


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PROTECTION

TSUNAMI

MEASURES


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¡YES!

¡NO!


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HOW SHOULD WE PROTECTOURSELVES FROM TSUNAMIS?

As you already know, a tsunami usually originatesfrom a large earthquake. Therefore, if you are in acoastal area when an eartquake occurs you shouldquickly move to a higher land or tough building,as soon as possible.

It is impossible to fully protect any coast from theravages of tsunamis. Countries have builtbreakwaters, dikes and various other structures totry to weaken the force of tsunamis and to reducetheir height. In Japan, engineers have built broadembankments to protect ports and breakwaters toprotect narrow harbor mouths in an effort to divertor reduce the energy of the powerful waves.

But no defense structures have been able toprotect the low-lying coasts. In fact, barriers caneven add to the destruction if a tsunami breaksthrough, hurtling chunks of cement about likemissiles.

In some instances, trees may offer some protectionagainst a tsunami surge.

The most important thing is to protect yourself andyour family by following these actions:

• If you perceive the severe shocks of anearthquake, don't stay watching or collectingshells from the beach, leave the beach and movequickly to a location that is more than 30 metersabove mean sea level.

• If there is no high ground near your location,protect yourself in a forest, or a tough building.

IF YOU ARE AT THE BEACH


46 I INVITE YOU TO KNOW THE EARTH II

47

IF YOU ARE AT HOME OR AT SCHOOL

DO YOU KNOW?

If you staycalm and followthe giveninstructions,no damage fromthe tsunami willbe experienced.

If there is a tsunami, I must:

• Follow instructions given by authorities.

• Keep away from the beach and otherlow lying areas and go to a place morethan 30 meters above mean sea level.

• Keep away from rivers.

• Take with me a portable radio, ablanket, food and drinking water.

• Follow instructions given by the authoritieson radio and TV.

• Go quickly to a place at an elevation morethan 30 meters above mean sea level or toa forest.

• Keep away from rivers.

• Take with you a portable radio, a blanket,some food and water for drink. Nothingelse.

• If your are with adults, remind them to takea first aid kit.

• Do not return home until authorities saythat the tsunami is over.

• If you are far from your family, you shouldgo to the previously established meetingplace.


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Blank Page


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GRAVITY METER

STRAINMETER

SEISMOGRAPH

MAGNETOMETER

RESISTIVITY METER

LASER RANGEMEASURES

DRAWINGS OF INSTRUMENTS TO CUT OUT


I INVITE YOU TO KNOW THE EARTH II - PreventionWeb

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