ED 216 911

AUTHORTITLE

INSTITUTIONSPONS AGENCYREPORT'NO

DOCUMENT RESUME

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Stoeve, Edward C., Jr.Earthquakes and Plate Boundaries. Crustal EvaluationEducation Project. Teacher's Guide [and] StudentInvestigation.National Association of Geology Teachers..National Science Foundation, Washington, D.C.)CEEP-MOD-MD1-4-2; ISBN-0-89873-012-0;ISBN-0-89873-013-979SED-75-20151;'SED-77-08539; SED-78-2510419p.Ward's Natural Science Establishment, Inc. P.O. Box

PUB DATEGRANTNOTEAVAILABLE FROM

SE 038 115

1712, Rochester, NY 14603 (or P.O. Box 1749,Monterey, CA 93940.)

MF01 Plus Postage. PC Not Available from,EDRS.*Earth.:Science; Geology; Instructional Materials;Oceanography; *Science Activities; *Science CourseImprovement Projects; Science Curriculum; ScienceEduca!tion; Science Instruction; Secondary Education;*Secondary School Science; *Seismology; TeachingGuides; Teaching Methods

IDENTIFIERS *Crustal Evolution Education Project; Earthquakes; .

National Science Foundation; *Plate Tectonics

EDRS PRICEDESCRIPTORS

ABSTRACTCrustal Evolution Education Project (CEEP) modul s

were designed to: (1) provide students with the methods an resu tsof continuing investigationsvinto the composition, hiitFiy, andprocesses of the earth's crust and the application of this knowledgeto man's activities and (2) to be used by teachers with little or noprevious background in the modern theories of sea -floor spreading, ,

continental drift, and plate tectonics. Each module consists of twobooklets:- a teacher's guide and student investigation. The teacher'sguide 'contains' all of the information present in the studentinvestigation. booklet as well as: (1) a general introduction; (2)prerequisite student background; (3) objectives; (4) list of requiredmaterials; (5) background information; (6) suggested approach; (7)procedure, including number of 45-minute class periods required; (8)

summary questions (with answers); (9) extension activities; and (10)list of -references. In this 2-period,module, students studyearthquake depth and distribution patterns around the world and therelationship between earthquakes and various types of 'plate'boundaries. The activities require observational, recording,plotting, and inference-making skills and serve as an' introduction toplate tectpnic theory or as a follow-up activity after a 'unit onearthquakes. (Author/JN) *,

************************************************************** ********Reproductions supplied by EDRVare the best that can be made

N* from the original document.***********************************************************************

Y

NAGT Crustal Evolution Education ProjectEdward C. Stoever, Jr., Project Director

Welcome to tne exciting world of current researchinto tr'07! composition history and processes of theearto s crust and the application of this knowledgeto ma^ s activities The earth sciences arecurrently experiencing a dramatic revolution. in

,hierstanding of the way in which the earthCEEP modules are designed to bring into

tre assroom the methods and results of theseinvestigatiDns The Crustal Evolution

-_.- Project began work in 1974 under1-- fspis:es of the National Association of

Teachers CEEP matenals have been.leeloosed Cy teams of science educators ,

sssr om te.aCh.'S and scientists Prior to.f--,lication the materials Olerpi field tested by

ran 2`-.) teachers and over 12 000 studentsC .rren c:r...sta evolution research is a breaking

5*_.dents are tnrougn 'oday

About CEEP Modules...two booklets a

Teah-e. and a Student Iniestigation TheTeac'er s CL.de all the information

nc: vstrations ne Student investigationvs seol ions Orl^teg color .ntenaed only for the

'eacher s 1rei as anserS to the questions thatar=-' InCluried n the StAent InvestigationIn S(VMP "iodides tnere are illustrations that

om,,/ ne Teacher s Guide and these areles.gmated ty figure letters instead of the number

,ence Jsed in the Stjdent InvestigationFor some mocii.vies maps rulers and other

C-Jrnmr)r, C:aSSr')Orn materials are needed-and ip

7

The ,,,aterial wAoprepared with thesupport of flti.onal Science FoundationGrant Nos SED 75-20151 SED 77-08539and SED 78-2S104 However, any opinions,findings conciusionssor recdmrnendaticinsPxoressed nereir are those of the author(5)and do not necessarily reflect the flews

NSF

In order tO comply with U S Piibilc Law94 86 P,eri SCh00' district in the U S A,sing 'hese -haterials agrees to makethem available for inspection by parents orguardians of children engaged ineducational programs or projects of theschool district

Pl Copyright 1479 by Southeast Missouri Stet* University

t

Teachers and students alike have a uniqueopportunity through CEEP modules to Oare in theunfolding of these educationally important and

, exciting advances CEEP modules are designedto prchide students with appealing firsthandinvestigative experiences with concepts which areat or close to the frontiers of scientifiw inquiry intoplate tectonics Furthermore the CEEP modulesare designed to be used by teachers with little'orn previous background in the modern theories-inf sea-floor spreading continental drill- and platetectonics

We know that you enjoy using CEEPm:-/-_Juies in your tiassrc.)o?'n Read on and be-_.rrbared to experience a renewed enthusiasm for

vo,, t.7,arn more about the living eartha^d )'her CEEP modules

g_.ant:ties,acc9rding to the method of;presentation Read over the module beforeschedufing Its use in class and re.fer to the 119t ofMATERIALS in the module

Ear r,.moni_de Is individual and self-contained inc-inteht out soe are divided into two or more:mils for convenience She recommended lengthof time for eacn module is indicated Some modulesr-'cluire DrerequiSite t,4.rioviledge of some aspectsof basic earth science this is noted in tneTr?acher s Guide

Earthquakes AndPlate Boundaries

.-

INTRODUCTIONIn this activity, the student studies earthquakedepth and -diOribution patterns around the worldand the relationship between earthquakes andvarious types-of plate boundaries. It la anexercise InvolVIng observation, recording, plottingand inference-making based on observation.It should be useful as an introduction to platetectonic theory, or as a follow-up activity aftera unit on earthquakes.

Why do earthquakes occur where they derWhat causes earthquakes? Are earthquakesrelated_ to any earth structures? The earth's outershelrof rock is ,belleved to be made up of anumber of rigid plates, called lithospheric plates,which are from 80 km to 160 km thick Theplates are made up of the two upper-rock zonesof the earth, the crust and the upper portion ofthe mantle (Figure 1). Some plates include onlyoceanic crust. Other plates include .both oceanic '4and the lighter continental crust. These platesride on a zone in the mantle where the rock isalmost melted and therefofe not rigid Anexample to help you picture this would be a blockof wood floating in a bowl of honey.

In this activity you wilt find out that differentpatterns of earthquakes and topography arerelated to different kinds of plate bolindanes

PREREQUISITE. STUDENT BACKGROUNDAlthough this activity is intended to serve asan early introduction to the concept of lithosphericplates, you should provide sorne,backgroundknowledge of earthquakes and how epicentersare located. Activities similar to Imfestigation16-4 in Investigating the earth (3rd ed., 19,78)would provide helpful liackground material inunderstanding how tline-travel curves areused in locating the ei3icenter, of anearthquake:

OBJECTIVESAfter you have completed this activity, you shouldbe able to:i: Explain the methrld,Osed to find the locationand depth of earthquakes on the World

.Setsmic.ity Map.2. Explain the relation,ship`between earthquakesand plate boundaries.3. Make a graph showing the distribution ofearthquake depths near a coast, given

cation and deptnof eartnquakes.,.:

4

Ocean

Crust

, 4

kMantle

--O km\ .\

\.Strong sheliifhtposphere,

80-160 km

,Weak sne,slasthenosonere,

Not to scale

Figure 1 The rigid lithospherid plates and theirrelationship to the outer rock zones of theearth ,(Thickness of zones not to scale )

-

4. Describe the distribution of earthquakedepths in an area where continental and oceanicpl4tes collide5. Describe the relationship between earth-quakes and major geographic features inSouth America6. Interpret data to identify the type of plate-boundary in a.given area.

1

Earthquakes AndPlate Boundaries

INTRODUCTION _ _

In this activily, they student studies earthquakedepth and -ditribution patterns around the worldand the relationship betWeen earthquakes andvarious types-of plate.boundaries. It ks anexercise frivolling observation, recording,,,plottingand inference-making based on observation.It should be Useful as an introduction to platetectonic theory, or as a follow-up activity aftera unit on earthquakes.

Why do earthquakes ocdur where they derWhat causes earthquakes? Are earthquakesrelated to any earth structwes? The earth's outershellof rock is' believed to be made up of a .

number of rigid plates, called lithospheric plates,which are from 80 km to 160 km thick' The -44.1/4

plates are made up of the two upper'rock zonesof the earth, the crust and the upper portion ofthe mantle (Figure 1) Some plates include onlyoceanic crust. Other plates Include both oceanic irand the lighter continental crust. These platesride on ozone in the mantle where the rock isalmost melted and therefofe not rigid Anexample to help you picture this would be a blockof wood floating in a bowl of honey

In' this aativity you wilrfind out that differentpatterns of earthquakes and topography arerelated to different kinds of plate boUndaries

PREREQUISITE, STUDENT BACKGROUNDAlthough this activity is intended to serve, asan early introduction to the concept of lithosOhericplates,you should provide sorne,backgroundknowledge of earthquakes and how epicentersare located. Activities similar to Inicestigation16-4 in Investigating the earth (3rd ed., 1q78)would provide helpful background material inunderstanding how tline-travel curves areused in locating the etsicenter of anearthquake: \OBJECTIVES

11

After you have coinpleted ,this activity, you shouldbe able to:1: Explain the methded,Osed to find the locationand depth of earthquakes on the World

.Seisnycity Map.2. Explain ttae relation,ship'between earthquakesand plate boundaries.3. Make a graph showing the distribution ofearthquake depths near a coast, given the', -

rationand depth.of earthquakes:

Crust

'Ocean

,

manpe.

.0 kri

,Strong Shelll(Iltoospnere

80-160 km

,Weak she'fasthenoso,,ere.

/

Not to scale

Figure 1 The rigid lithosphend plates and their. .

relationship to the outer rock zones of theearth (Thickness of zones not to soale

-c

4. Describe the distribution of earthquakedepths in an area whete continental and oceanicpl4tes collide5. Describe the relationship between earth-quakes and major geographic features inSouth America .

6. Interpret data to identify the type of plateboundary in a..given area.

6

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MATERIALS17-1;:---World Se lsmlcIty Map (obmpiled by ArthurTarr), United Stater Geological SurI4ey, 1200S. Eads Street, Arlington, VA 22202i-one for eachgroup of four students, or several per classroom.Map, The PhySiaal World, National GeographicSociety, Educational Services, Department79, Washjngton, D.C. 20036one for classroomColored pencilsfor each student

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BACKGROUND INFORMATION _ -

The earth's surface is composed of seven majorplates which are about 80 km to 16%km thick.These rigid plates are made up of the lighterrocks which form the earth's crust and denserrocks of the uppermost portion of the mantle. The,crust and upper mantle are called the lithosphere.The plates of the lithosphere ride on a lessrigid layer of rock, deeper in the mantle, calledthe asthenosphere. Rock in the asthenosphere isalmost at its melting point and therefore hassome plastic[properties, The plates ride likegiant rafts on the asthenosphere.

Along these major plate bounof geologic activity takes pla reat stressesbuild up in these zones as one plate edge pressesagainst another. Eventually the stress becomes,too great and the plates move against eachother, causing an earthquake. See Figures

'3, 4 and 5. Ktiowledge of where earthqual*occur can help identify the location and typesof boundaries of the major plates of the earth.

Although it may now seem rather simple todraw a line through earthquake epicenters, theearthquake information required to definethe natureAof plate boundaries took many yearsof careful reccird-keeping.

5 I

Several major/types of plate boundaries are (hylpothesized:1. Spreading boundaries where the lithosphereis moving apart, as along the oceanic ridges(Figure 2).2. "Ifransform boundaries where plates are slidingpast each other (Figure 3).3. Boundariet of convergence where' platescollide, causing buckling and upthru4ting ofthe crustal plates (Figure 4).4. Boundaries of dubduction where plates havingcontinental crust collide with plates havingoceanic crust, causing the leading edge ofthe plate with oceanic crust td be thrust under theleading edge of the one with continental crust(Figure 5).

es a great deal

IS!

2

Study of these plate boundaries shows thatspreading,boundaries are under tension, transforniboundaries show lateral or sliding motion andconvergent and subduction boundaries areunder coMpression.

Figure 2 Plates may mcve apart from oneanother MagTa rises upward into mid-oceanridge

"VAPROK47-9.f.4;:?''JZ:fA

Figure 3 Plates may move past one anotherOne block of crust is transparent to show lopationof earthquakes (foci)

/

r.

c.

Figure 4 Plates with coVinental crust maycollide with one another

Figure 5 A plate with oceanic crust may collidewith a plated with continental Crust Magmarises upward into mountains

4 Oc ea ^ c cJst

Illustration Key

Hthospherei

p0

Eartiquake depths vary depending on the typeof plate boundary:1. Along spreading boundaries earthquakesare shallow.2. Where plates slide past each other (as alongthe San Andreas Fault), earthquakds are shallow..3. Where plates are colliding, most earthquakesare shallow, some are of intermediate depthand, occasionally, deep ones occut.

A very clear pattern of earthquakes, ranging fromshallow to deep, is found wriere plates bearingoceanic crust collide with platen beatingcontinental crust. These earthquakes mark thesubduction zone of the descending plate whichcontains the denser oceanic crust. The oceaniccrust that is being pushed (subducted) down intothe mantle descends at an angle of from 30'to nearly 90i(usually about 45-).

By plotting the depth of focus of earthquakeswhere continental crust and oceanic crustare colliding, students will be better able tounderstand the contact made by the crustal platewhich is plunging down into the mantle.

The Peru-Chile trench is viewed by earthscientists as a classic ocean floor trench causedby a colliding of the Nazca and American plates.Similar trenches, which ring the Pacific Oceanbasin, form the deepest surface features on earthand are frequently associated with earthquakesand volcanic activity.

SUGGESTED APPROACHStudents should work in groups of four, witheach group having the World Seismicity Map

and a map showing major featurets of the oceanbasins, such as TIA Physical World map.Although less desWable, students could referto maps posted around the room if enough mapsare not available for each group. Up to a thirdof a class period will be require for studying theWorld Seismicity Map before t questionscan be answered.

Discuss the'World Seismicity Map with thestudents before they begin work, so they will befamiliar with the symbols and will know whattype pf information is found on the map.Make sure students understand the four typesdf plate boundaries. Otherwise, little can be

learned from the rest of the activity. Do not spenda great deal of time going over the details andinterpretations of the Seismicity map withthe entire class. Answers to the questions arebest handled in the small group settings.

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3

You should plan on one to two 45-minute classperiods for the completion of this activity,depending upon the ability and previous back-.ground of students. It ;is suggeste'd that thestudents'progresg,and answers to the questionsbe evaluated while they are working in groups. '

The profile that students develop does not hqldfor all ocean trenches. In some places, the/deeper foci forma steeper slope than theshallowei foci, suggesting that the crustal platemay become contorted after passing intothe asthenosphere.

PROCEDURE s

In the first part of this activity, each groupof students will work with a copy of the WorldSeismicity Map. Interpretation of the map'snotation and the pattern of earthquake distribu-tion are primary objectives of this part ofthe activity.Key words: oceanic crust, continental crust,mantle. lithospheric plates, epicenter, focusTime required: two 45-minute periodsMaterials colored pencils, World Seismicity Map,The Physical World map

A great deal of action takes place along adjacentplate boundaries Large forces buird up asone plate movas with respect to another Whenthe force becomes too great, the rocks moveagainst each other, caysing an earthquakeDifferent types of mov ent of adjacent platesmay occur Plate boun nes are the sites ofmuch earthquake activi ,Boththe pattern ofearthquake distribution and major topographicfeatures are distinctive of the type of plabteboundaries and motion (see Figures 2, 3, 4, and 5)

Look at a copy of the World Seismicity MapNote Please do not mark on this map Otherstudents must use it Before proceeding, carefullyread the box on the map entitled'EXPLANATION

1. The dots on this map represent earthquakesthat occurred over a period of time of nineyears and six months

2. Large earthquakes are represented bycircles , smaller earthquakes by dots

The focus of an earthquake is the point withinthe earth where an earthquake actually occursThe epicenter of an earthquake is the point onthe Dearth's surfacewhich lies directly abovethe focus. See Figure 6

3. Which of these two points is represented bythe location of the dots on the map shwing ,

earl h qua kes9

The epicenter locations

4

I

EaonaJa.e Aave*-7,-4s,

Figure 6 Focus and epicenter of earthquake

4. On the map, what color is used toindicateearthquakes ofa a shallow focut'(0-70 km)? redb an intermediate focus (71-300 km)9 greenc a deep fOcus (301-700 km)'' blue

Scientists.,believe that /zones of frecipentearthquake activity are thc result of movementsalong plate boundaries Vany 'of .the earth'ssurface features are associated with plateboundaries See whep the locations of epicentersare located oh the World Seismicity Map Thenfind tkeilocations of ocean ridges and trencheson The Physical World map

5. List at least two `major kinds of ocean floorfeatures which seem to 'coincide with the locationof Major zones of earthquake activityDeep sea trenches and mid-ocean ridges

6, Where dogralos't of the earthquakes occur inSouthRmenba9On tne.western coast in the countries of Peruand Chile.,

List one kind of continental feature which seemsto be :related to frequent earthquakesmountains

7

Data in Table 1 show the lbcation, and depth ofearthquake activity along the west coastof SouthAmerica near the Tropic of Capricorn.

.7.plot the data on the graph on Worksheet,!using colored pencils for each range of depth,as shown on the World Seismicity Map. Thenanswer the questions which follow.

,Table 1Location and depth of earthquake foci,

for plotting on WorksheetDatumPointNo

Depth(km)

Distance (km)and direction'

from coast

DatumPointNo,

Depth(km)

Distance (km)and direction

from coast

1 50 .0 12 50 100 East2 300 100 Est 13 300 500 East3 385 450 East 14 485 280 East,4 60 80 East 15 660 550 East5 125 250 East 16 90 90 West6 200 70 East 17 520 200 East7 690 400 East 118 90 25 West8. 25 40 West 19 44() 600 East9 500 700 East 20

Elt66p East

10 515 385 East 21 100 West11 380 340 East 22 75 100 West

of Capr corn

CEEMIIIMEiklERNIMISEESOMEZIERIMMIELIESEMEEMESIEREESINIMEMINEMEMIENESSESIBI

Answer Sheet

0 c

1

4

_VC ..

cl00

West 100 0 100 .200 300 400 500 600

Distance west or east of coast irk kilometers

100

200

.300

400

500

600

700

700 East

5

8, Describe the relationship between the location-of the epicenters (east or west) and the depthof focus of earthquakes along the coast of SouthAmerica, as shown by-your graph 'The earthquakes are shallow near the coastline(focus less than 70 km). Going eastward toward ,

th?-center of the continent, the earthquakefoci become deep9. Descnb&the type of plate boundary whichyou thirlk is present along the west coast of SouthAmericaThe type of boundary along the west coast ofSouth America is thought to be a subduction

undary, i.e., where a plate having 'oceanic crusts colliding with a plate'having continental crust.ote. The student graph is representative Of

the boundary, and students should be cautionedthat it is probably better thought of as

'a zone than as a line.

FolloW the zone-of earthquake activity, fromSouth America northward past Central America,as shown on the World Seismicity Map.

SUMMARY QUESTIONS *1. From what you have learned in thiscactivity,draw a cross section of what you think the profileof the continent and ocean plate boundarymight look like along the west coast of SouthAmerica (Hint look at Figures 2, 3, 4, and 5 )On this sketch, show and label the location of thedeep Chile-Peru triench and the volcanic mountains(the Andes)Based upon their investigation in this'activity,students should be able to sketch somethingsimilar to this diagram.2. In what way is the plate boundary along the

,coast Of California different from the plateboundary along the west coast of South America?The distribution of earthquake foci along the "coast of California suggests a vertical plateboundary similar to that shown either in,,Figure2 or in Figure 3. Since the California earthquakezone is bounded on one side by continental crust,this boundary is best represented as the typeshown in Figure 3.

On the other hand, the plate boundary along thewest coast of South America is a collision -typeboundary sinillar to that shown in Figure 5. Thiis evident from the existence of an oceanictrench and a zone-of earthquake foci Inclineddownward under the edge ofghe coriiinentalcrust.

4\6

i

/

N,

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10. Where does the plate boundary appearto change?By looking at the earthquake activity hortnwardalong the western coastline of South and CentralAmerica, it is notigeable that the depths of ,

foci become shallower. Northward from southernMexico virtually all the earthquake activity hasa shallow focus. It is interpreted that the shallowfocus earthquakes are a result of a change inthe type of the plate boundary.

11. Offer a possible explanation fo his change.),t)n the vicinity of southeroNexico, he plateboundary along the west coast of South Americaand Central America, appears to terminateagainst another plate boundary, which can betraced continuously along the East Pacific Riseand western margin of North America. This canbe inferred from the distribution orclustersof earthquake foci.

.

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Figure A. Sample student diagram of a crosssebtion of the west coast of South America:

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EXTENSIONS1. What type of plate boundary do you thinkwould best account for the type of earthqUakeactivity found in California?Sliding motion, as would be found along atransform boundary, could account for the -earthquake activity in California. (Refer studentsto Figure 3.)

2. Locate three other areas on the earth's surfacewhich would most likely haye plate boundariessirniUar to the one in South America. Explainthe eason for your choices.Most of the Pacific Ocean Plate is borderedby plate boundaries similar to the South Americanboundary. Notable examples are along theAleutian Island's, the islands of Japan, the MarianaIslands, and the Samoa-Tonga-Kermadec Islandsnortheast of New Zealand. However, notelhatin the New Hebrides Islands: west of theSamoa Islands, the usual pattern is reversed, andearthquake foci become deeper toward the PacificOcean basin, rather than away from it. In thisregion, the Australian Plate, interpreted tobe moving rapidly northward, is being overriddenby the Pacific Plate, thereby reversing the shallow-to-deep earthquake focus sequence.

3. Locate three areas on th arth's surfacewhich appear to have bound ries similar to thekind shown in Figure 2.Areas along mid- oceanic ridges wouldpaveearthquakes similar to the kind shovOnFigure 2. ,

4. Locate one area on the earth's surface whichappears to have boundaries similar. to the kindshown in Fig6re 4.The Himalayan mountain range is an exampleof an area which has a boundary similar tothe kind shown in Figure 4. This is an area wheretwo plates of continental crust are collidingalong a boundary of convergence.

REFERENCESAG!, 1978, Investigating the earth. 3d ed., Boston,

Houghton Mifflin Co.'Canby, T.Y., 1973, oalifornia's San Andreas

Fault. tioNanal Geographic, v 143, no. 1 (Jan.1,p. 38-53.

Press, F., and Stever, R., 1974, The earth. SanFrKicisco, W.H. Freeman and Co.

Science Year: The World Book Science Annual,. 1973 ed., s v. Earth's heat en Ines: (he forcethat moves continents, by Deffeyes, K.S.,p. 163-187.

Wyllie, P.J., 1976, The way the earth works. NewYork, John Wiley and Sons, Inc. 296 p.

Young, P., 1976, Drifting continents, shiftingseas. New York, Franklin Watts, Inc.

V.

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NAGT Crustal EvolutionEducation Project ModulesCEEP Modules are listed here in alphabeticalorder. Each Module is designed for uSe_inthe number of class periods indicated 'Forsuggested sequences of CEEP Modules tocover specific topics and for correlationof CEEP Modules to standard earth sciencetextbooks, consult Ward's descriptiveliterature on CEEP The Catalog Numbersshown here refer to the CLASS PACKof each Module consisting of a Teacher's

`Guide and 30 copies of the StudentInvestigation See Ward's desciiptiveliterature kir alternate order quantities

r:opyright 1979 Except for the rights tomaterials reserved by others tpepubs Sher and the copyright owner herebygrant permission without charge todomestic persons of the U S and Canadafor use of this Wolac and related materialsin the English language in the U S andr;anaria after 1985 For conditions of useand, permission to use the Work or any partthereof for foreign publications orPublications in other than the Englishlanguage apply to the copyright owner orpublisher

I

CEEP ModuleClass CLASS PACK

Periods CatalOg No.

A Sea-floor Mystery: Mapping 3 34 W 1201Polarity Reversals

Continents And Ocean Basins: 3-5 34 W 1202Floaters And Sinkers

Crustal Movement: A Major Force 2-3' 34 W 1203In Evolution

Deep Sea Trenches And Radioactive 1 34 Itif 1204Waste

Drifting Continents Apd Magnetic 3 34 W 1205Fields

Drifting Continents And Wandering 4 34 W 1206Poles

Earthquakes And Plate 2 34 'W 1207Boundaries . .

Fossils As Clues To Ancient 2. -3 34 W 1208Continents (

Hot Spots In The Earth's CrustHow Do Continents Split Apart?How Do Scientists Decide Which Is

The Better Theory?Hqw Does Heat Flow Vary In The

Ocean Floor?

3

2

2

2

34 W 120934 W 1210

I 34 W 1211

34 W 1212

How Fast Is The Ocean Floor 2-3 34 W 1213Moving?

Iceland; Tje Case Of The Splitting 3 '34 W 1214Personality

Imaginary Continents: A Geological 2 34 W 1215Puzzle

Introduction To Lithospheric 1-2 34 W 1216Plate Boundaries

Lithospberic Plates And Ocean 2 34 W 1217Basin Tdpography

Locating Active Plate Boundaries 2-3 '34 W 1218'By'Earthquake Data

Measuring Co,ntinental Drift: The 2 34.W 1219Laser Ranging Experiment

Microfossils, Sediments And 4 34 W 1220Sea-floor Spreading

Movement Of TI-re Pacific Oceanfloor

2 34 W 1221

Pkaiso Boundaries And Earthquake 2 34 W 1222Predictions

Plotting The Shape Of The Ocean 2-3 34 W 1223Floor

Quake Estate (board game) 3 34 W 1224

Spreading Sea Floors And Fractured 2 34 W11225Ridges

The Rise'A-nd Fall Of The Bring 2 34 W 1227Land Bridge

Tropics In Antarctica? 2 34 W 1228

j Volcanoes: Where And Why? 2 34 W 1229

What Happens When Continents 2 34 W 1230Collide? . .

When A Piece Of A Continent 2 34 W 1231Breaks Off

*WhiCh Way Is Norjh? 3 34 W 1232

Why Does Sea Level Change? 2-3 34 W 1233

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1111111111Ward's Natural Science Establishment, Inc.P.O. Box 1712, Rochester, New York 14603 P.O. Box 1749, Monterey, California 93940 -

.CUP MODULE NO. MDI 4-2ISBN: 0-U171-0124 Printed In U.S.A.

CRUSTALEVOLUTION,EDUCATION

PROJECT

NAME

Studeilt investigationCatalog No 34W1107

Earthquakes' AndPlate Dounddrie

a

DATEa

4

INTRODUCTIONWhy do earthquakes occur wherethey do?What causes earthquakes? A' earthquakesrelated to any earth structures? The earth's outershell of rock is believed to be made up of anumber of rigid plates, called lithospheric plates,which are from 80 km to 160 km thick. Theplates ace made up of the two upper rock zonesof the earth, the crust and the upper portion ofthe mantle (Figure 1). Some plates include onlyoceanic crust. Other plates include both oceanicand the lighter continental crust. These plates_ride on zone in the mantle where the rock isalmost melted and therefore not rigid Anexample to help you picture this would be-a blockof wood floating in a bowl of honey.

In this activity you will find out that differentpatterns of earthquakes and topography arerelate() to different kinds of plate boundaries

at

4

OBJECTIVESAfter you have completed this activity, you shouldbe able to:1. Explajn themethod u3ed to find the locationand depth of earthquakes on the WorldSeismicity Map,2. E5plain the relationship between earthquakesand plate boundaries3. Make a graph showing the distribution ofearthquake gepths near a coast, given thelocation and depth of earthquakes.

copyrognt 1979 by Southeast Missoun State tintverstty

1

rust

Mantle

Ocean

0 km

N4-1) scale

Strong shellIlithospherel

80-160 km

Weak shell\

(asthenosphere)

Figure 1 The rigid lithospheric plates and theirXtionship to the outer rock zones of theh. (Thickness of zones not to scale.)

4. Describe the distribution of earthquakedepths in an area where continental and oceanicplates collide.5. Describe the relationship between earth-quakes and major geographic features inSouth America6. Interpret data to identify the type of plate .boundary in a given area.

1

ti

pft DURE

Materials: colored Rencits. World Seismicity Map,The Physical Wor/drnap

A great deal of action takes place-aftmg adjacentplate boundaries. Large forces build up a sone plate moves with respect to another. Whenthe fOrce becomes too,great, the rodks movedgainst each other:causing an earthquakeDifferent types of. movement of adjacent platesmay occur. Plate boundaries are the.sites ofmuch earthquake activity. Both the pattern, ofearthquake distribution and major topographicfeatures are distinctive4t the type of plateboundaries'and motion (see Figures 2, 3, 4, and 5).

Figure 2. Plates mpy. move apart from one"'another Magma ries upward into mid-oceanridge

Figure 3. PlatesOne block of crusof earthquakes (to

2

ay move past one another.transparent to show location

-

Figure 4. Plates with continental crust maycollide with one another

Figure 5..A plate with oceanic crust may collidewith a plate with continental crust Mipmarises upward into mountains

/

tntinental crut

Oceanic crust (lithosphere)

Upper mantle

Mantle (asthenosphere)

Earthquake

I 0 Illustration Key

Lo at a copy of the World Seismicity Map.Xote: Please do not mark on this map. Otherstudents must use it. Before proceeding: carefullyread the'box on the map entitled"EXPLANATION.".

7,

1, The dots on this map represent earthquakesthat occurred over a period of time of

years and months.,

2. Large earthquakes are represented by, smaller earthquakes by

The focus of an earthquake is the point withinthe earth where an earthquake actually occurs.The epicenter of an earthquake is the point onthe earth's surface which lies-directly abovethe focus. See Figure 6.

3. Which of these two points -is represented bythe location of the dots on the map showing

earthquakes?

4. On the map, what color is used to indicateearthquakes ofa *a shallow focus (0-70 km)?b an intermediate focus (71-300 km)?

c. a deep focus (301 -700 km)?

Scientists believe that zonesof frequentearthquake activity are the result of movements

along plate boundaries. Many Of the earth's.surface features are associated with plateboundaries. See where the-locations of epicenters

are ltcated on the World Seismicity Map. Thenfind the locations of ocean ridges and trenches

-on The Physical World map.

5. List at least two major kinds of ocean floorfeatures which seem to coincide with the locationof major zones of earthquake activity.

5

Fault Focus -E'arthquage wave fronts"

Figure ,6 FocuS and epicenter oreaithquake..

6. Where do most of the earthquakes occur in

South America?

AID

List one Find of continental feature which seems-

to be related to frequent earthquakes.

3,

Data in Table 1 shoW the location and depth ofearthquake activity along the west coast of Southi?trrrericia near the Tropic of Capricorn,

1. Plo?,the data on the graph on Worksheet,using cplored pqncils for each range of depth,as shown on the World Seismicity Map. Then

0 answer the questions which follow.

Table 1.- Location and depth of earthquake foci

for plolting on Worksheet%.m....0. eratum Depth Distac)ce (km)

Point (km) and directionNo fro coast

1 50 02 300 '111 ast3 385 450 i ast

60 80 st5 125 250 E st6 200 70 Ea .t7 690 400 Eat8 25 40 Wet9 500 700 East

10 515 385 East11 380 340 East

P.

Worksheet4

Tropic of Capricorn

DatumPointNo

Depth' Distance (km)(km). and direction

from coast12 50 100 East13 300 500 East14 485 280 East15 660 '550 East16 90 90 West17 520 200 East18 90 25 West19 440 '600 East20 640 660 East21 50 100 West22 75 100 Wiest

Tropic of Capricorn

A

MMEEMEIMNIE ---_,4,--; BkIEMIENECIE

IMUMEIMBEMEMEIENIFSE-MiMEEMEINI

_-_-. ___-:---1W---EMILIEEMEIE

{ZEIBMISEME, .---

West 100 0 100 200 300 400 500 6006

Distance west or east of coast in kilometers

I 6 -

0

100'

200

300

400

500

600

700

700 East

O

8: 'Describe the relationship between the locationof the epicenters (east or welt) and the depthof focus of earthquakes alort the coast of South

-di America, as shown by your graph.

9. Describe the type of plate boundary whichyou think is present along the west coast of SouthAmerica

For low the zone of earthquake activity, fromSouth' America northward past Central America,as shoWn on the World Seismicity Map.

10. Where does the plate boundary appearto change

175

11. Offer a possible expilahation for this change.

SUMMARY 'QUESTIONS1. F m what you have learned in this activity,draw cross section of what you think the profileof the continent and ocean plate boundarymight look like atong the west coast of SouthAmerica (Hint look at Figures 2, 3, 4, and 5 )On this sketch, show and label the location of thedeep Chile-Peru trench and the volcanic mountains(the Andes)

2. In what way is the plate boundary along thecoast of California different from the plateboundary along the west coast of South America'?

18

f

EXTENSIONS1. What type of plate boundary do you thinkwould best account for the type of earthquake

4111activity found in California?

2. Locate three other areas on the earth's surfacewhich would most likely have plate boundariessimilar to the one in'South America Explainthe reason for your choices

REFERENCESCanby, T.Y., 1973, California's San Andreas

Fault. Nationpl Geographic, v. 143, no. 1 (Jan.),

p. 38-53. 1

Science Year: The World Book Science Annual,1973 ed., s.v. Earth's heat engines: the forcethat moves continents, by Deffeyes,p. 163-187.

di --

3. Locate th'ree areas on the earth's surfacewhich appear to have boundaries,. similar to thekind shown in Figure 2

4. Locate one area on the earth's surface whichappears to have boundaries similar to the kindshown in Figure 4

1 !Ip 7