earthquakes volcanoes and tsunamis

The Cracked Egg In this experiment you will use a boiled egg to simulate the ior of the tectonic plates on the earth’s surface... Just like the pieces of the eggshell in the egg experime

Earthquakes, Volcanoes,

and Tsunamis

Projects and Principles for Beginning Geologists

budding scientists study how they work?

Through experiments, models, and

demon-strations This in-depth resource will teach

readers how to build a seismograph to

record a simulated earthquake, compare

pressure waves and shear waves—the two

types of ground shocks—using a Slinky,

and replicate a tsunami’s destructive effect

on a “coastline” built in a bathtub

Authors Matthys Levy and Mario Salvadori

even discuss issues of modern architecture

and civil engineering: how science can be

used to protect buildings and property in

earthquake-prone areas

Earthquakes, Volcanoes, and Tsunamis

answers a wide array of questions about

these phenomena Can animals “predict”

earthquakes? How have various cultures

explained the movement of the earth

throughout history? What is the Richter

scale, and what does it tell us about the

strength of a quake? And most important,

readers will learn how to earthquake-proof

their homes, and how to protect

them-selves should they experience a tremor

Matthys Levy is a civil engineer and the inventor

of the Tenstar Dome, which is used to cover athletic

venues around the world Mario Salvadori was a

professor of architecture and the founder of the Salvadori Center, an educational nonprofit devoted

to teaching youth about math and science through hands-on study of structure and architecture.

Earthquakes, Volcanoes,

Library of Congress Cataloging-in-Publication Data

1 Earthquakes—Juvenile literature 2 Volcanoes—Juvenile literature.

3 Educational games—Juvenile literature I Salvadori, Mario,

1907-1997 II Levy, Matthys Earthquake games III Title.

QE521.3.L486 2009 551.2—dc22

2008040143

Cover and interior design: Scott Rattray

Interior illustration: Christina C Blatt

Cover photos: iStock

© 1997, 2009 by Matthys Levy and Mario Salvadori

All rights reserved

First published in 1997 by Margaret K.

McElderry Books as Earthquake Games

This edition published by Chicago Review Press, Incorporated

814 North Franklin Street

Chicago, Illinois 60610

ISBN 978-1-55652-801-9

Printed in the United States of America

5 4 3 2 1

To the children of P.S 45 in the Bronx, New York,

who fi st asked,

“Mario, how do earthquakes work?”

And to Nicola, Okna, Shae, Edison, Austin, Daniel, and Maia

M L and M S.

Preface vii

1 The Secrets of the Earth 1

䉴 The Cracked Egg 4

䉴 Wave Refraction 42

䉴 The Strength of Water 43

5 How Strong Was It? 45

䉴 Build a Seismometer 47

䉴 A Pendulum 51

䉴 Another Pendulum Experiment 54

䉴 The Seismograph 56

6 From Myth to Science 65

䉴 The Shaking Experiment 66

䉴 Making Predictions 70

䉴 Mapping the Risk 74

7 Can Animals Predict Earthquakes? 79

8 Should We Fight or Fool the Quakes? 83

䉴 Another Volcanic Eruption 108

䉴 Build a Cardboard Volcano 110

䉴 A Smoking Volcano 112

䉴 Geothermal Energy 117

Conclusion 121 Appendix: Important Earthquakes, Volcanoes, and Tsunamis 123 Resources 131

Index 133

e expect many things to move, but not the earth!

How could the earth, which is strong enough to port a skyscraper, shake and break up? Where do earth-

sup-quakes come from? Are we ever going to know when and where they

will hit? And co uld we e ver l earn to b uild str uctures capable ofwithstanding earthquakes?

Many years have passed since humans fi st experienced quakes Over time, we have learned answers to most of these ques-tions—but not all of them

earth-The book is b uilt around projects, demonstrations, and simpleexperiments that make it easy and fun to develop a physical under-standing of earthquakes and their natural relatives—volcanic erup-tions and tsunami waves You will enjoy working on most of theseprojects alone or with a friend; for a few, you may want to ask a par-ent or an older sibling or friend to help you In either case, you willhave a good time and also learn a lot about earthquakes, volcanoes,and tsunamis

W

Preface

We hope you will enjo y reading this book as much as w e didwriting it, but above all, we hope that you will never meet face-to-face with an earthquake, an erupting volcano, or a tsunami.

NO OT TE E:: Although English units of measurement (feet, pounds, etc.)are still commonly used in the United States, almost all the othercountries in the world have adopted a measurement system called

the metric system or SI This system is taught in o ur schools and is

the official me asurement system of our fe deral g overnment Forthese reasons, all the measures in this book are given fi st in met-ric units, then in the equivalent measures in English units

3.28 feet = 1 meter

We all liv e on th e surface of the e arth, but did y ou ever

wonder what goes on beneath the surface, deep inside theearth, dee per than th e dee pest mine? No human beinghas ever been do wn there, but e arth scientists have been a ble tolearn a lot about what it’s made of and what goes on inside the bigsphere on which w e live And a t the same t ime, their discoverieshave helped to e xplain much of the mystery of how earthquakeshappen and volcanoes erupt

Imagine that the earth is like an apple or a peach and consists

of a skin, a “meaty” part, and a core or pit The core of the earth is

solid metal (iron and nickel) surrounded by hot liquid metals The

The Secrets of the Earth

1

1

“meat” of the earth, the mantle, is a h ot, somewhat soupy mass of melted rock called magma The skin of the planet is its crust, the

hard surface of the earth on which we live

The crust is not equally thick all around the earth It is as deep

as 40 kilometers (25 miles) under the surface of the continents and

as thin as 5 kilometers (3 miles) under the ocean flo r

Crust

MantleLiquid core

Solid core(1,250 km/775 mi.)

2,200 km 1,364 mi.

2,900 km 1,798 mi.

Until recently the crust was assumed to be solid rock, but coveries have shown instead that it is cracked into separate sections

dis-called tectonic plates Some of them are so large that they determine

the boundaries of entire continents or o ceans—one of the platessupports all of the United States, and the whole Pacific Oc an sits

on another Other sections are small er, supporting only part of acontinent o r a small g roup of islands, like th e pla te under th eCaribbean

The Cracked Egg

In this experiment you will use a boiled egg to simulate the ior of the tectonic plates on the earth’s surface

1 Put enough cold water in a pot to cover an egg With the help of

a parent or other adult, bring the water to a boil

2 Lower an egg into the boiling water with a spoon Turn the heat down to a low boil and cook the egg for about 7 to 9 minutes

3 Take the egg out of the water and cool it under cold water The egg should be medium cooked, not hard.

4 Strike the boiled egg gently against a hard surface, like the top of

a kitchen table, and break the eggshell into a number of pieces, some large and some small They will be the tectonic plates of your “earth.”

5 If you now squeeze the egg gently between two fingers, the

“plates” will move Some will bump against adjoining plates, ers will slide along them, and some will move away from each other A plate may even slide under an adjoining plate.

oth-N OTE : Since the consistency of a boiled egg varies depending on

its age, the suggested boiling time is approximate and you may have to proceed by trial and error to be successful with this experiment.

Just like the pieces of the eggshell in the egg experiment, theseparate tectonic plates flo ting over the magma don’t stay put butmove around at a snail’s pace , at only 50 millimeter s (2 inches) ayear As th ey move toward each other, one plate may hit an other(top left), slide along it (top right), or even duck under it in a move-

ment called subduction (bottom).

2 Push your knuckles together, and at the same time try to make one hand slide with respect to the other The harder you push your knuckles together, the harder it will be to make your hands slide; you will feel the stress increase along your knuckles, just

as it increases between the rough edges of the plates

3 If you keep pushing for a while, the muscles of your “plates” will start hurting because the knuckles are preventing the sliding But eventually one “plate” will suddenly slide, releasing the energy accumulated in your hands This is how an earthquake happens

From the time our planet fi st came into being about fi e lion years ago, somewhere on earth two plates under the continentshave bumped and pushed against each other, neither of them giv-ing in; they pushed and pushed, and eventually bent up the earth’scrust This is how they created high mountains—and still do

bil-The Birth of Mountains

You can feel how mountains form through this demonstration

“earthquake.”

3 But if you keep pushing harder and do not slide one hand under the other, your fingers will bend up, creating “mountains.” The middle fingers form the highest mountain; call it Mount Everest (or, by its Tibetan name, Chomolungma, Goddess Mother of the World) It is the highest mountain on earth, at 8,848 meters (29,029 feet) high Your ring fingers in this experiment represent the second-highest mountain, K2 (or Godwin Austen), which is 8,611 meters (28,251 feet) high Your index fingers form Kanchenjunga, the third-highest mountain on earth at 8,598 meters (28,209 feet) high.

N OTE : The height of these three mountains is actually increasing

yearly by several millimeters as the Indian plate pushes against the Eurasian plate.

Along the plate boundaries where one plate dips below another,such as wh ere the Pacific pl te dips bene ath the North Americanplate, the edge of the lower plate plunges down into the incrediblyhot mantle and melts If a crack already exists in the crust at thatpoint, the pressure from the weight of the crust pushes up the boil-ing hot melted rock, the magma, through the crack This is how avolcano is cre ated Be cause th e e arth’s cr ust is so much thinnerunder the oceans, many more volcanoes are gener ated there than

on the surface of the earth

Ocean

crust

ContinentalplateMagma

When two tectonic plates move away from each other, also mostoften at the bottom of the ocean, a crack opens in the earth’s crustthrough which magma is squeezed up in volcanic eruptions, creat-

ing a ser ies of underwater mountains called ridges The one place

on earth where this kind of crack passes through land and you canactually see these ridges being born is on the island of Iceland

Ridges

Water levelIslands

CrustCrust

Magma

Ever since th e e arth’s cr ust hardene d, e arthquakes ha veoccurred, not all over the earth’s crust but mainly along the edges

of the tectonic plates The most active earthquake areas are along

the r im of the Pacific Oc an, called the circum-Pacific belt, which

starts in Japan and circles the Pacific Oc an, bringing devastation

to Alaska, the West Coast of the United States, and S outh ica, as well as Southeast Asia Earthquakes also occur along a stripfrom Portugal to Australia cutting through Italy, Greece, Turkey,

Amer-and Iran, called the Alpide belt.

Falling Towers

To show how earthquakes can damage buildings and kill people, trythis demonstration

3 Imagine that the towers were actual buildings resting on tectonic plates How devastating can an earthquake be?

Some earthquakes are w eak and do n ot do too much dama ge,but th e wo rst can destro y entire cit ies and kill th ousands up onthousands of people The most deadly ever, which struck Tangshan,China, in 1976, killed more than three hundred thousand people.

At the present time, most of the residents of the United Statesare lucky: strong earthquakes and volcanic eruptions occur mainly

on the West Coast But in the past there have been de adly quakes in th e East and in th e Mid west, as th e do ts on th e mapbelow show

1 Since nobody has been inside the earth, which is so hot that whoever tried would be burned to death, how can we know so much about it?

When two tectonic plates hit each other in a subduction, they sendout “signals” called seismic (e arthquake) waves, which can be

“heard,” just as we can hear the sound waves from a faraway sion Because the waves travel at different speeds through the dif-ferent materials that make up the earth (see chapter 4), listening tothe seismic wa ves has allo wed earth scientists to deter mine whatthose materials are

explo-2 I have heard that the continents move over time Will

we, anytime soon, be able to walk from the United States to France?

Not unl ess you plan to liv e a long , long t ime! Bu t you are co rect—the con tinents are belie ved to once ha ve been all joine d

r-together as one b ig continent called Pangaea, which then cracked.

The se ctions (our present continents) dr ifted apar t and are n owbeginning to move together again If this movement continues foranother 200 million y ears, the continents will be clo se enough tobuild a bridge between New York City and Lisbon, Portugal

3 If the tectonic plates are floating on the soupy magma, wouldn’t they tilt if we built all of our cities

on one coast?

No, the earth’s crust is so h eavy that what we build on it is lik e a

f y on an el ephant But, as a ma tter of fact, the continents do t ilt

over t ime as th e te ctonic plates push a gainst one an other Th eNorth Amer ican con tinent t ilts to ward th e e ast, causing th ebeaches on th e East Coast of the United States to get small er asthose on the West Coast get bigger.

4 When red-hot magma flows out through cracks in the earth’s crust under the middle of the ocean, doesn’t it immediately harden when it reaches the cold ocean water, just like melted wax or chocolate hardens when poured into cold water?

Yes, as ma gma re aches th e water its surface hardens , f orming acrust that cr acks as it is con tinuously pushed up b y h ot magmabelow The ridges that form on the bottom of the ocean, therefore,have a very cracked-looking surface

Imagine that you were alive about two hundred years ago Your

family was thrilled when they heard that President Jefferson hadpurchased th e Lo uisiana T erritory, an are a b igger than th eentire United States at that time, and they decided to establish anew h ome in th e wil derness You didn’t kn ow wha t to e xpectwhen you left your old home and friends in the city of Philadelphiaand traveled westward until you reached the shore of the giantMississippi River, south of what is now St Louis To begin yourtrek into the new territory, you had to wait for a boat to take youacross the river Finally, in early December 1811, your father found

a boatman willing to take you and your whole family across withall your possessions

If You Had Been There

2

17

High up on th e far shore, you helped your family build a porary sh elter, wh ere you wo uld sp end your fi st winter in th ewilderness While it was still dark on the morning of December 16,your dog became restless and started moaning and baying, wakingyou out of a sound sleep You pushed him away to try to get back

tem-to sleep, but suddenly the ground began tem-to rumble and shake—andyou were scared stiff The timbers of your shelter creaked and theground rose and fell as if it were an o cean wave, continuing forwhat felt like an eter nity Outside, you could hear the trees g roan

as they were bent by the force of the passing wave While waitingfor the sun to r ise, you stayed huddled together with your family,not knowing what to expect next After dawn another shock struck,

and you could see the ground boiling, jets of sandy water shooting

up into the air A crack appeared in the ground and you were afraidyou might fall in it, but fortunately it closed rapidly, leaving only ascar on the face of the earth

As you looked across the river, you saw that the steep bluff onthe far side had slid do wn to th e riverbank and tha t waves weresweeping up and do wn th e r iver Th e boat you had cro ssed th eriver in just a fe w da ys e arlier was wash ed up on sh ore andsmashed A sand y island ne ar the middle of the river had disap-peared; it had completely sunk below the water’s surface

For close to a month, shocks almost as strong as the fi st tinued You and your family, who had thought you were starting anexciting new life in a peaceful territory, were instead living a fright-ening nightmare You had survived the most powerful earthquakeever to strike the United States

con-At this p oint, you may very well wonder h ow such an e quake could have occurred in the Louisiana Territory in the center

arth-of the United States, which is in the middle arth-of a tectonic plate Youread in th e fi st chap ter tha t e arthquakes take place along th e

boundaries of tectonic plates What happened?

Even seismologists—scientists who study earthquakes—have not

been able to answer this question with absolute certainty But theybelieve that a deep-rooted crack exists in the middle of the NorthAmerican plate and tha t th e 1811 e arthquake was cause d wh enthis fracture shifted

And why did your dog “feel” the earthquake before anyone else?

Animals seem to be sensit ive to precursors, vibrations and so unds

that pre cede an e arthquake and tha t we ourselves cannot feel o rhear You will be amazed at how sensitive animals are to earthquakeprecursors when we explore the issue in chapter 7

And why did the island disappear in the middle of the river? Itdid so because when sand is fil ed with water and is shaken by an

earthquake it liquefies, or fl ws as if it were a liquid.

2 Next, add water to the sand-filled pail until it reaches the very

level of the sand surface, thus saturating the sand with water.

3 Now shake the pail, as you did before you poured in the water.

This time, the brick will slowly sink into the sand, tilting or pling over or even disappearing The brick behaves like a tall

top-building on mushy soil and shows how the water acts as a cant, allowing the brick to slide into the sand.

lubri-The same ph enomenon takes place wh en a b uilding is set onweak soil and, par ticularly, on soil ne ar a sandy seashore where it

is completely saturated Liquefaction is a very dangerous enon in earthquake areas

in a strong e arthquake, but rocky soil will n ot Clay soil be comes

“soapy” under heavy rains, although it is a good soil when dry If ithasn’t been done before, it may be advisable for your parents to havethe soil and the foundation under your home checked by an expe-rienced contractor or engineer

2 We live in Japan in a high-rise apartment building

I am nervous thinking about the possibility that our building could fall down What could happen?

The Japanese government—and all governments, for that matter—are trying to guard against something terrible happening by mak-ing certain that builders follow strict rules to make buildings strongenough to remain standing in an earthquake Some years ago, dur-ing an earthquake in Niigata, Japan, an apartment building built onsand that liquefi d tilted almost totally on its side with out break-ing up so that the occupants could safely reach the ground by walk-ing do wn th e facade On th e o ther hand, in a mo re re cent,disastrous earthquake in Kobe, Japan, the earth shook so violentlythat many apartment buildings on soft soil collapsed

In chapter 1 you learned that the magma of the earth’s mantle is

very hot Because the temperature is n ot the same thro ughout

the mantle, the magma develops hot rivers that move in circular

motions, rising and falling under the earth’s crust

When the Ocean Rolls

3

25

䉴 2 pieces of toasted bread, 50 mm (2 in.) square

1 With the help of a parent or other adult, place a pot of water on the stove and turn on the heat.

2 When the water boils, drop a few grains of rice into the pot

3 Watch carefully as the water pushes the grains of rice in a lar motion, up the sides of the pot, then away from them near the surface of the water, then down to the bottom in the center of the pot, and finally back up the pot’s side The grains of rice are

circu-moved by convection currents, just as the hot rivers of magma

move around the mantle.

4 Now carefully drop two squares of toasted bread into the water.

Notice that the pieces of bread move toward the center of the pot, and that sometimes one piece of bread rubs against the other, while at other times one piece dips under the other

This experiment demonstrates how tectonic plates are dr iven

by convection currents and move about our planet, causing quakes when they bump into each other and opening cracks called

earth-rifts through which magma fl ws up.

You have alre ady l earned that wh en th e e dges of two platesscrape against each other, an e arthquake will o ccur The edges ofmost tectonic plates do n ot lie on land b ut under th e seas, whichcover over 70 p ercent of our planet W hen one pla te push es upsuddenly against another at the bottom of the sea, the shock alsopushes up a mo und of water As th e mound settles down, a wa ve

called a tsunami (after th e J apanese wo rd f or “se ashore villa ge

wave”) moves out in all directions on the surface of the ocean, likethe waves that radiate from a pebble thrown into a pond

Generating a Tsunami

You can reproduce this ocean phenomenon the next time you take

a bath in the tub

You’ll Need

䉴 bathtub

1 Fill a bathtub with water.

2 Once the water surface is level, slowly lower your open hand close to the bottom of the tub

3 Now move your hand up rapidly a short distance You have ally “moved up” part of the water at the bottom of the tub, and you should see the surface of the water move in tsunami waves

actu-You may at one t ime have made a circular wa ve appear on th ecalm waters of a pond by tossing a stone into it, then watched thewave move outward in bigger and bigger circles What you may nothave noticed is that as the circular wave moves outward on the sur-face of the pond, the water particles of the pond move brief y up anddown but remain where they were before you dropped the stone Youcan easily check that the water particles stay put by noticing that asthe wave goes by, a leaf lying on th e pond’s surface moves up anddown, but does n ot follow the wave’s outward movement (facingpage) This happens because a wave is the motion of the water shapebut not of the water particles in the direction of the wave

Tsunamis start as waves at most 1 meter (3 feet) high Kn ing this, you may reasonably feel that tsunamis cannot be too dan-

ow-gerous In fac t, tsunamis are extremely dangerous, be cause th ese

waves are man y kilometer s long and th e enormous energ y theyreceive from th e sudden shift ing of the se a flo r moves them atspeeds of up to 600 kilometer s (400 mil es) per hour This allo wsthem to cross entire oceans before crashing ashore

As a tsunami wave travels toward shore, it changes shape as thelower part of the wave is slowed down by the friction between thewater and th e se a flo r, whil e its top , unrestr ained by fr iction,moves faster and faster and incre ases in h eight as th e se a flo rslopes up When the wave reaches the shore, a tsunami ma y be awall of water 30 meters (100 feet) high

When th ese incre dibly p owerful waves, th ese walls of water,final y crash on th e shore, they destroy beaches, harbors, houses,and anything else in their path It is because these waves smash intoseaside villa ges that th e Japanese name d th em “se ashore villa gewaves.” If they hit a harbo r, they may throw the anchored shipsonto the land and destro y the docks When they hit the mouth of

a river, they run inland along th e river valley, playing havoc withhouses, destroying vegetation, and killing people and animals Thenthe tsunami r ushes back down the valley, carrying into the oceanthe ruins of the villages and the bodies of its victims

䉴 6 bricks

䉴 many small wooden cubes, about 25 mm (1 in.) on each side

䉴 square sheet of plywood, about 300 mm (1 ft.) on each side

1 Fill a bathtub with 100 millimeters (4 inches) of water To avoid scratches, place a tub mat on the bottom of the tub, near the faucet end.

2 Set two piles of two bricks each on the tub mat, 300 millimeters (1 foot) from the faucet end Leave a gap of 50 millimeters (2 inches) between the two brick piles

3 Place the last two-brick pile on the mat about 150 millimeters (6 inches) behind the other two (almost under the faucet).

4 Set another tub mat in front of the bricks to generate friction at the bottom of your “tsunami.”

5 Build a number of “buildings” with the wooden cubes on top of the three two-brick piles.