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CascadiaGPSAnalysisTeacherInformationandAnswerKey Page1

CascadiaGPSAnalysis:TeacherInformationTechnologyisamazing.TheGlobalPositioningSystem,knownasGPS,hasbeenaroundformanyyears,anditsapplicationsaremany.Inanutshell,GPScanbeusedtolocatewhereyouareontheEarthwithinafewmeters,andpeoplearemostfamiliarwithGPSunitsincarstohelpwithdirections,orforrecreation,likehiking.AspecifictypeofGPScalleddifferentialGPS,ordGPS,isextremelypreciseandcanbeusedtoshowtectonicplatemovementofmillimeters!

Basically,thereare24GPSsatellitescruising12,000milesabovetheEarthmovingatabout7500kilometersperhour.That’salmost2kilometerspersecond–yes,2kilometerseverysecond.Thesatellitessendoutradiowavesignalsinalldirections.Receiverscantellhowlongittakesfortheradiowavestoreachthem,andusingsomemath,computerscancalculatethedistancebetweenthereceiverandthesatellite.Computerscanthentranslatesmallchangestolargechangesbylookingatlargerintervalsoftime.

dGPSissomuchmoreaccuratebecauseitusessomeverysophisticatedcomputingtotakeouterrorsduetotheatmosphereandinaccurateclocks,forexample.ThepictureonthestudenthandoutshowsaGPSMonument.InsidethedomeistheGPSantennathatreceivestheradiowavesandsendsthesignaltoanattachedreceiver.TheresultingpositionaldataarethensentviaInternettoUNAVCOforfurtherprocessing.Scientistscanthenuselong-termpositionaldatatointerpretplatemotionsandplateboundaryinteractions.NGSSSTANDARDALIGNMENTDisciplinaryCoreIdeas•MotionandStability—ForcesandInteractions:HS-PS2-1,MS-PS2-2•Energy:MS-PS3-1,MS-PS3-2,HS-PS3-2,MS-PS3-5•WavesandTheirApplicationsinTechnologiesforInformationTransfer:HS-PS4-2,MS-PS4-3,HS-PS4-5•Earth’sSystems:5-ESS2-1,HS-ESS2-1,MS-ESS2-2,HS-ESS2-2,MS-ESS2-3,HS-ESS2-3•EarthandHumanActivity:HS-ESS3-1,MS-ESS3-2ScienceandEngineeringPractices CrosscuttingConcepts4.AnalyzingandInterpretingData5.UsingMathematicsandComputationalThinking6.ConstructingExplanationsandDesigningSolutions

2.CauseandEffect4.SystemsandSystemModels7.StabilityandChange

LESSONPLANThisisamulti-daylesson,andcouldtake2–3lessons(hourlong)tocomplete.IRISEducationandOutreachhasatwo-partvideotodemonstrateallpartsofthisactivity:http://www.iris.edu/hq/inclass/video/gps_monitors_deformation_in_subduction_zone_part_1_introhttp://www.iris.edu/hq/inclass/video/gps_monitors_deformation_in_subduction_zone_part_2_using_real_data


Introduction:Havestudentsstandupandtrytoonlymoveamillimeter.Witheverymovement,sayit’stoomuch.ThiswillimpressuponthemtheaccuracyofthedGPSsystem.Thesatellitesystemcandetectmovementsofpartsofcontinentsmovingmillimeters.

PARTI:BuildingaGPS‘Monument’

Materials:• Sharptoothpicksworkbest.• Gumdropscanbefoundatlargerstoreswithbulkcandy.Canalsousethesmaller‘spicedrops’available

atmoststores,butit’stoughertogettoothpicksin.• Onlysmallamountsofmodelingclayarenecessary.• Transparenciescanbecutintoquartersheets.Youcanevenusesmallerpiecesifnecessary.Cuttingone

sheetinto6thshouldbelargeenough.Procedure:1. Buildingthemonumentshouldtakeafewminutes,andit’sthehook.Studentswillusethegumdrop

modelforPartII(ifdoingPinpointingLocationportioningroups),andalsotomodelstationmovementinPartIV.

2. Havestudentsplacegumdropmonumentinmiddleoftransparencysheet.Clayrepresentstheconcretethat‘glues’themonumenttoEarth’ssurfacerocklayersbeneaththesoil.

3. Studentscanalsodrawandcoloronthetransparencysheettorepresentrocklayers.Thekeyisthatstudentsunderstandthatit’scrustalrock,notjustthemonumentorsoil,thatmoves.

4. Ifdoingtheactivityovertwodays,havestudentswritetheirnameonapieceofscrappaperandplacegumdropmonumentontoptosavefornextday.

PARTII:PinpointingLocation

Therearethreemethodstodothedemonstration,whichvaryinscale.OptionOne–SmallerScaleSupplies:• 3ringstands(withoutrings)• 3‘satellites’toplaceattopofringstands.BubbleYumgumhasashapesimilartoGPSsatellitesandisan

attentiongrabber.Youcouldalsoprintsmallpicturesofsatellitestotapetotopofringstands.• Stringsof3differentlengthstapedtotopsofringstands–allmustbeatleastaslongasheightofring

stands• GumdropmonumentfromPartIDemonstrationProcedure:1. Premarklocationsofringstandssothatall3stringsmeetinonelocationontablesurface.Youwillhave

tosetthisupandcutthestringsbeforehand.2. ExplainthatsatellitesareflyingaboveEarth’ssurfaceatsamealtitudeandringstandsrepresentthat

height.


3. Explainrelationshipbetweengumdropmonument(builtinPartI)andsatellite–they‘talk’toeachotherandestablishthedistancebetweenthem.

4. Thestringrepresentsthedistancebetweenthesatelliteandmonument.5. Haveastudentcomeandmoveonestring(heldtautly)inalldirectionstoindicatethatthedistanceis

known,butthedirectionisn’t.Aspherearoundthetopoftheringstandisestablishedwithradiusequalingthedistancefromthesatellite.

6. Haveanotherstudentmovea2ndstringaroundandnotewherestringsintersect–thereisacircleofpossibleplacesthishappens.Emphasizeagainthattheonlyknownentityisthedistancebetweenthemonumentandsatellite.

7. Haveathirdstudentmovethe3rdstringtoshowwhereall3stringsintersect.Thereshouldbetwoplaces–oneonEarth’ssurfaceandoneinspace–whereall3stringsintersect.Notethatcomputerscanautomaticallydetectthattheoneinspaceisnon-sensical.

8. Placethegumdropatthepointwhere3stringsintersect.9. Remindstudentsthatthesemeasurementsaretakingplacewhilesatellitesaremovingat2

kilometers/second!10. HavestudentscompletePartIIquestionsonworksheet.Note:activitycanbedoneingroupsfollowingsamedirections.

OptionTwo–LargerScaleSupplies:• 3longlengthsoftwine(constructiontwineworksfine)thatwillreachfromhighuponthewallstoa

centralpointsomewhereintheroom.• Tapetoholduptwineonwall.• 3‘satellites’toplaceattopofringstands.BubbleYumgumstillwillwork.Youcouldalsoprintlarger

picturesofsatellitestotapeonthewalls.• GumdropmonumentfromPartI,oralargerversionofaGPSmonument.DemonstrationProcedure:11. Tapeendsofstringsonwallssothatall3stringsmeetinonelocationsomewhereonthefloorofthe

room.Youwillhavetosetthisupandcutthestringsbeforehand.12. Coilupthelongstringsandtapethemuponthewallsoyoucaneasilypullthemdownandhandtoa

student.13. Followsameprocedureasaboveforlocatingthethreeplaceswhereall3strings(distances)meet.

OptionThree–LargestScaleDemonstrationProcedure:14. PresentdemonstrationjustaswithOptionTwoabove,onlyusemuchlongerstringandusethegymor

outdoorbasketballhoops.

Hereisavideoyoucouldalsouse:

https://www.youtube.com/watch?v=IoRQiNFzT0k


PARTIII:MeasuringCascadiaGPS/TectonicMovement

Procedure:

1. Reviewmetricsystem(millimeter,centimeter,meter,kilometer).2. Reviewcardinaldirections.3. TherearehundredsofdGPSstationsinoperation.4. Instructstudentshowto‘read’aTSP.UseexamplefromPacificBeachasexampletodoaswhole

class.5. Verticalisnotusedbecauseitismoredifficulttodetermineachangeinaltitude.Imagineasatellite

overheadlookingforside-to-sidemotion,andthentryingtodetermineverticalmotion.Itwouldbemuchmoredifficulttoseetheup/downmotion.

6. Witharuler,drawalineofbestfittoshowtrendofTSP.Trytodrawthelinesothatthereareanequalnumberofpointsaboveandbelowtheline.Usingaclearrulerworksbest.

7. Usingy-axismmscale,determineoverallchangeinpositioningiventimeperiod.8. Calculateannualmovementbydividingoverallchangeinpositionbytotaltimeperiod.

DetailonInterpretingTimeSeriesPlots(TSP)

a) AllplotshaveaY-axiswith‘zero’andpositivenumbersabovethelineandnegativenumbersbelowtheline.Numberlesstickmarksontherightmirrorthemeasurements.

b) The‘North’plotshowsNorthandSouthmovement–anythingmovinginthe‘positive’(up)directionismovingNorth,andanythingmovinginthe‘negative’oroppositedirectionismovingSouth.

c) ThesameistrueforEast/West–movementinapositivedirectionismovementtotheEast,andanythingmovinginthenegativedirectionismovingWest.

d) Mosttimeseriesdonotincludegridlines,soit’shelpfultousearulerorstraightedge(aclearoneisbest)tocalculatehowmuchmovementthereis.

e) Thescaleontheaxeswillvaryandtheunitsmayvaryaswell.f) UsuallyN/SandE/Wmovementiseasiertoseeapatternwithcomparedtoheight.Butremember

thattherearealotoferrorsthatmustbecorrected,sothedatawon’talwaysbeperfect,orinaclearpattern.

g) Thedataintheexamplesareverylinear–usuallythey’realotmessier.h) Thetimescaleisshownbyyearsandtwelfthsofyears.i) Receiverscollectapositionalmeasurementeverysecond.That’s86,400measurementsaday.These

areaveragedtogetonepointforeachdaythatshowsuponatimeseries.j) Mostplotsnowstartrightat‘0’onthey-axis;whatisimportantisthechangeinposition.However,

sometimesyouwillneedtousethetrendlines,notthepoints,todeterminechangeinposition.k) ThemovementsthatdGPSreceiversshowareverysmall–millimetersorcentimetersatmost.But

justthinkhowmuchmovementthatwouldmeanoverthousandsofyears!Aneasyequivalenttorememberis1mm/yristhesameas1kilometer/1millionyears.


AnswerstoStudentWorksheetareshownbelowonAnswerKey.

PARTIV:PlottingGPSStationMotionProcedure:1. Followproceduresonstudenthandout.Confusionmayariseaboutscaletranslationofcentimetersto

millimeters.Scaleusedonthegridiscentimeterstomakegraphingeasier.Actualmovementisinmillimetersbutthisisfartoohardtoseeat1:1scale.

2. VectorgraphshouldlookliketheexampleprovidedonAnswerKey.Colorsusedmayvary.3. TheGPSgumdropstationswillmovealongpathofvectors,mimickingthemovementofthetectonic

platewithGPSstationattached.Foraddedeffect,have3studentsputtheirgumdropmodelsonONEmap(page7ofthestudentworksheet)andthensimultaneouslyhavethemmovethegumdropstheappropriatedistancealongthevectorinthesametimeperiod.Althoughcramped,itshowstheshorteningeffectofthewesternmarginquitewell.PARTV:AnalysisofGPSStationMotionThebigpictureresultoftheactivityisthatcoastalstationsofOregonandWashingtonarebeingpushedtowardthenortheastatabout1/2ofthevelocityofJuandeFucaPlatemotionwithrespecttointeriorNorthAmerica.Urbancorridorstations(inWillametteValleyofOregonorPugetLowlandofWashington)arebeingpushedtowardthenortheastatabout1/4ofthevelocityofJuandeFucaPlatemotionwithrespecttointeriorNorthAmerica.StationseastoftheCascadesarenotmovingatallorarebarelymoving.TheclearimplicationisthatcoastalareasaremovingtowardseasternareasastheactivecontinentalmarginisbeingcompressedinSW–NEdirection.StrainisbuildingwithinthePacificNorthwestmarginoftheNorthAmericanPlateastheJuandeFucaPlatepushestheNorthAmericanPlatemargintowardthenortheast.ThisaccumulatingstrainwilleventuallybereleasedinthenextgreatearthquakeontheCascadiaSubductionZone.TheplateboundaryregionsoftheJuandeFucaandNorthAmericanplatesare“lockedandloading”.Furtherimplicationsofthe“lockedandloading”natureofthePacificNorthwestcontinentalmarginareelasticenergywillbestoredupoverlongintervalsoftimeandthensuddenlyreleasedinthenextgreatCascadiaearthquake.Forexample,overtheaverage500yearsrecurrencetimebetweengreatearthquakes,thecoastalstationswillmovenortheastabout7.5meters(25feet).Duringthenextgreatearthquake,thestoredenergyduetotheslowNEmovementwillsuddenlybesuddenlyreleasedasthecoastalareasreboundthesamedistancetowardsthesouthwest.Procedure:1. LeadstudentstoanswersfromobservationsofthePacificNorthwestvectormap.2. Discussbigpictureafterstudentsrealizethattheregionisbeingsqueezed.3. Afurtherdemonstrationistakingapieceofpaperorclothandholdingtherightsideofitstationary,

andthenpushingtheleftsidetowardstheright.Thepaper/clothwillbuckle.


Name: CASCADIAGPSANALYSISToday’sDate:

PARTI:BuildingaGPS‘Monument’Materials: 4toothpicks,1gumdrop,modelingclay,ruler,1/4sheettransparencyProcedure: 1. Insert3toothpicksdiagonallyintothegumdrop.Thesewillactasthe

legs.2. Insertaslightlyshortertoothpickstickingstraightdownfromthemiddle

ofthegumdrop.Thetipofthistoothpickshouldbejustbarelyabovethesurface.Thiswillbethe‘placemarker’.

3. Putverysmallpiecesofclayonthebottomofthelegs(nottheplacemarker).TheclaywillactasacementtoholdtheGPSstationinplace.InrealitythelegsofaGPSstationarecementeddeepintothegroundsothatifthegroundmoves,sodoestheGPSstation.

4. PositiontheGPSMonumentontopofapieceofcleartransparency.PARTII:PinpointingLocation1. Whatdothetopsofthestringholdersonthewallsrepresent?2. Whatdoesthelengthofstringrepresent?3. HowmanysatellitesareneededtopinpointthelocationofaspotontheEarth?4. Whywouldn’toneortwosatelliteswork?Expainanddrawadiagramtoshowthis.5. Drawthesetupofthedemonstration inthespacetotheright.

Gumdrop

Toothpick

Clay

TEACHERANSWERKEY

Thetopsofthestringsrepresentwheresatellitesare–allareatthesameheightabovetheEarth.

Thelengthofstringrepresentsthedistancebetweenmonumentsandsatellites.

Atleast3satellitesareneededtopinpointthelocationofthemonumentonthesurface.Inrealitymorethan3areused.

Onesatellitewouldn’tworkbecausethestationcouldbeaninfinityofpointsaroundthatonesatellite.Twowouldn’tworkbecausethetwospheresaround2satellitesintersectataninfinityofpointsaroundthecirclewherethetwospheresintersect.


PARTIII:MeasuringCascadiaGPS/TectonicMovementMaterials: Coloredpencil(fordrawingtrendlines),clearruler,calculator• HighprecisionGPSstationscollectdatain3partsshowninTimeSeriesPlots(TimeSeriesorTSP):

o North/Southmovementovertime(abbreviatedN/S)o East/Westmovementovertime(abbreviatedE/W)o Height(up/down)movementovertime(notshowninthisactivity)

• X-axismeasurestime.• EachdotontheTSPsistheaveragepositionofthestationforoneday.

PacificBeach,WashingtonGPSData–CoastalStation

Thefirstthingtodoisdrawa“trendline.”Positionaruler(clearworksbest)sothatthetrendlinerepresentstheaverageoftheplotsaboveandbelowtheline.Drawthelinesothatitcrossestheaxesonbothsides.Notetheexampleabove.DrawatrendlinefortheEastportionofthePacificBeachTSP.6. Whataretheunitsofmeasurementforthesetimeseries?Circlethebestchoice. a) centimetersandmonths b) metersandyears c) millimetersandyears d) centimetersandyears

19961998200020022004200620082010201220142016

TrendLine


7. Ifeachdotistheaveragepositionforanygivenday,howlongofatimespanhasthisstationbeencollectingdata?

a) 10years b) 15years c) 19years d) 201/2years8. HowfarNorthdidthePacificBeachstationmoveonthetimeseries?Hint:calculatethechangein

positionovertime. a) 200millimeters b) 215milllimeters c) 230millimeters d) 275millimeters9. DidthestationmoveSouthovertheperiodoftimerelativetoitsstartingposition(1stmeasurement)? a) No,becausetrendlineonlymovesup. b) Yes,becausetrendlinemovesdown. c) Can’ttellfromtimeplotsgiven.10. HowfarEastdidthestation(andthereforetheEarthbelowit)moveontheTSP?Remembertousea

straightedgetohelp. a) 205millimeters b) 215milllimeters c) 280millimeters d) 300millimeters11. Whatoveralldirectionwasthisstationmoving? a) Northonly b) Northwest c) Northeast d) Southwest12. WhatwastheannualmovementintheNorthdirection?(Hint:Dividedistancetraveledby#ofyears) a) 10mm/yr b) 11.3mm/yr c) 16mm/yr d) 200mm/yr13. CalculatetheannualEastwardmovement: a) 4mm/yr b) 13.3mm/yr c) 14.7mm/year d) 280mm/yrUsingtheTSPsbelowforGrapeview,WAandLind,WA,calculateN/SandE/WmotionandanswerquestionsforeachTSP.Startwithdrawingtrendlinesthatcrossbothverticalaxes.

Notethatsomepositions(dots)are‘off’thegeneraltrend,orthereisagapinthedata.Thosemightbetimeswhenmaintenancewasbeingdoneonthestation,ortherewassomeerrorthatwasbeingcorrected.Youcanignorethosepointswhendoingyourtrendlinesandcalculations.


Grapeview,WashingtonGPSData–UrbanCorridorStation

14. Accordingtothisdata,howlongofatimeperiodhasthisstationbeeninoperation?Notethateach

smalllineonX-axisisonemonth,or1/12thofayear.15. WasGrapeviewmovingNorthorSouth?Howdoyouknow?16. HowfarNorthorSouthdiditmovesincedatahasbeenrecorded?17. Overall,wasGrapeviewstationmovingEastorWest?Howdoyouknow?18. HowfarEastorWestdiditmoveoverthewholetimeperiodofdatacollection?19. Werethereanytimeswhenthestationwasn’tmovingNW?Ifso,when,andwhatdirection??20. CalculateannualmotionsinN/SandE/Wdirections.

2004200620082010201220142016

May2005–Sept2016isabout11.5years

GrapeviewwasmovingNorthduetotheupwarddirectionontheN/Splot.IntermittentlyismovedS(down).

Itmovedapproximately56mmNorth.

GrapeviewwasmovingEastduetotheupwarddirectionontheE/Wplot.IntermittentlyismovedW(down).

Itmovedapproximately67mmEast.

ItmovedSouthwestinearly2007,mid2010,mid2011,early2014,andearly2016.

AnnualmotionsareNorth4.9mm/year(56mm/11.5yr)andEast5.8mm/yr(67mm/11.5yr)


Lind,WashingtonGPSData–EasternStation

21. Accordingtothisdata,howlongofatimeperiodhasthisstationbeeninoperation?22. WasLindmovingNorthorSouth?Ifso,howfar?Becarefulwithmeasurements.Usethetrendlineto

betterindicatethestartingposition.Hint:it’sbelow‘0’.23. WasOthellostationmovingEastorWest?Ifso,howfar?Again,becareful.24. WhataretheannualmotionsintheN/SandE/Wdirections?PARTIV:PlottingGPSStationMotionMaterials: CascadiaGPSAnalysisGrid(nextpageofpacket),3differentcoloredpencils,ruler

2004200620082010201220142016

May2004–Sept2016isabout12.5years

LindwasmovingveryslightlyNorth.Trendlineshowsit’sstartingat-1andmovingtoabout5,fortotalof6mm.

LindwasmovingveryslightlyEast.Trendlineshowsit’sstartingat-2andmovingtoabout12,fortotalof14mm.

AnnualmotionsareNorth0.5mm/year(6mm/12.5yr)andEast1.1mm/yr(14mm/12.5yr)


Procedure:1. Usingonecoloredpencil,startat(0,0)anddrawafaintarrowtoshowtheannualNorth

movementofthePacificBeachstation.

2. FromendpointoftheNortharrow,drawanarrowtoshowtheannualEastmotion.

3. Drawadiagonalarrowfrom(0,0)totheendpointoftheEastarrow.Thisfinalarrow(vector)showstheoverallannualdirectionandrateofmotionofthePacificBeachGPSstation.

4. Usingacentimeterruler,measurethelengthofthefinalvectorandlabelthevectorwithdistanceinmm/year.Note:Scaleongridiscentimeters,butactualmovementismillimeters–that’swhyyoulabel‘mm/year’.

5. Usingdifferentcolors,drawvectorsforGrapeviewandLindstations.

6. Completekeyindicatingcolorsofyour3GPSstationvectors.

KEY: Color StationLocation StationGroup(Coastal,UrbanCorridor,orEastern)

012345678910

11

12

13 TEACHERANSWERKEY

0123456789101112131415

EastwardVelocity(mm/year)

NorthwardVe

locity(m

m/year)

PacificBeach,WACoastal

Grapeview,WAUrbanCorridor

PacificBeach=18.5mm/yr

Grapeview=7.6mm/yr

Lind=1.6mm/yr

Lind,WAEastern


Procedure(continued):7. Placegumdropstation(ontopoftransparency)at0,0andmovethetransparencysheetalongoneofthe

Northeastvectorstosimulatethemotionofthelandatthatpoint.

PARTV:AnalysisofGPSStationMotion25. ThemapbelowshowsthedirectionandspeedofseveralGPSstationsinthePacificNorthwest.Whatdoyou

observeabout: a) thestationsalongthecoast? b) thestationsslightlyinland(Grapeview,Kelso,Corvallis)? c) stationseastoftheCascades(Wasco,Lind,LaGrande?26. Overtime,whatwillhappentothedistancebetweenstationsonthecoastandstationseastoftheCascades? a) Distancegetsshorter b) Distancegetslonger c) Distancestaysthesame27. WhatdoesthisindicateabouttheforcesactingonthePacificNorthwest?What’shappeningtotheedgeofthe

continent?

Newport Corvallis

Tillamook

PacificBeach

NeahBay

Kelso

Grapeview Lind

LaGrande

Wasco

TheyaremovingNEmustfasterthantheotherstationsinland.

TheyaremovingNEabouthalfasfast.

MovingNEjustbarely–almoststationary.

ThewesternedgeofthePNWisbeingpushedNEfasterthantheinlandareas.Asitdoesso,theregionisbeingcompressedinaNE–SWdirection.Theregionisbeingloadedlikeaspring.