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AnalysisofMagnitudevs.MercalliEffectivenessinMeasuringDamageofMajorEarthquake

EventsinContextofGlobalEconomy

AlexisVoeltner&VictorTruongAbstract

Earthquakescancausehugeamountsofdamagetocities.Thisstudywillexplorethe

relationshipbetweenanearthquakesmagnitudeandtheamountofdamageitdeals.Thereare

manyotherfactorstoconsiderwhentryingtodeterminehowmuchdamageanearthquakewill

cause,includingthelevelofinfrastructure,development,populationdensityandgeologyofa

region.Thestudywilllookattenearthquakesfromdifferentcountriesaroundtheworld

representingdifferentlevelsofdevelopmentandwealth.UsingArcmaptocreatechoropleth

mapstoshowcontrastbetweenareaswithdifferentpopulation,wealthanddevelopment,the

studyfoundthatareaswithmoredevelopedinfrastructureandwealthsufferedahighercostin

damagesbutasubstantiallyloweramountofdeathsandinjuries.Inreverse,areaswithlow

developmenttendedtosustainlessdamagesfinanciallybutinsteadsufferedahugedeathtoll.

Thisstudywillshedsomelightonhowdifferentregionsintheworldwillbeimpactedby

earthquakes.Thestudyconcludedthatthereiscorrelationbetweenanearthquakesmagnitude

andthedamageitdoestocitiesnearbybuttheMercalliindexisamuchbetterindicationofthe

amountofdamagedealt.

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Introduction

Earthquakescanbeoneofthemostdevastatingandcostlynaturaldisasters.In2010

alone,25earthquakescaused226,735fatalities,7.2millionvictimsand$46.2billionofdamages

(Guha,2010).Thepurposeofthisstudywastofindouthowstrongofarelationshipexists

betweenanearthquake'smagnitude,mercallirating,andregionaleconomytotheactualdamage

done.Populationdensity,wealthanddevelopmentofanareawereallkeyfactorsinthis

correlation.

TheRichterscaleisthewellknownandcommonlyusedtowayexpresstheenergy

releasedfromanearthquakeevent.TheRichterScaleisnotintendedtoexpressdamagedone.

Anearthquakeinadenselypopulatedareawhichresultsinmanydeathsandconsiderable

damagemayhavethesamemagnitudeasashockinaremoteareathatdoesnothingmorethan

frightenthewildlife(Bellis,2015).However,becauseofitswideacceptance,highermagnitudes

areoftenassociatedwithmoredamage,evenifthisisnotthecase.TheMercalliscaleisa

classificationofintensitythattakesintoaccountthelevelofshakingobservedbypeopleand

includesanintensityderiveddamagescaleinitsmeasurements.Peoplewhoexperiencean

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earthquakecangoonlineandshareinformationaboutitseffectstohelpcreateamapofshaking

intensitiesanddamagecalled,CommunityInternetIntensityMaps(USGS,2005).However,

becauseofthesubjectivityoftheseobservations,theintensitygiventoanearthquakeandthe

actualdamagedonemaynotbethesame.

Theexpectedresultsarethatthemagnitudewillbeaninaccuraterepresentationofthe

intensityofearthquakesbecauseitdoesnottakeintoaccountthevariabilityofpreparednessin

differentcommunities.Sensitive,lowerGDPcommunitieswillfeeltheeffectsofanearthquake

withgreaterintensitythanmorepreparedcommunitiesandthedamagewillthereforebe

underrepresentedbythemagnitude.ItisexpectedthattheMercalliIndexwillbemoreaccuratea

representation,butmaypossessinaccuraciesaswell,duetosubjectivemeasurementtechniques.

Methods

ThisstudyusedearthquakedatawithbothRichterScalemagnitudesandMercalliindex

ratingsforearthquakesthatoccurredfrom1970to2002.Thedataalsoincludednumberof

deaths,injuriesandcostofstructuraldamagesinmillionsofdollars.Itwasdecidedthatonly

earthquakeswithamagnitudeof4orhigherwillbeconsideredinthisstudybecauselow

magnitudeearthquakesdonottypicallycausesignificantamountsofdamage(USGS,2012).The

numberofearthquakesthatisbeinglookedatwasnarroweddownbygettingamapofpopulated

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areasandcreatingabufferzone.ThestudyusedahighresolutionSedacshapefileofpopulated

areastofindonlyearthquakesthatoccurredwithin30milesofametropolitanarea.Someofthe

earthquakesinthestudyweremissingdataontheMercalliindexsotheyweredeletedtoretain

onlyinformationonearthquakesthatshowedbothmagnitudeandMercalliindexdata.Itwas

decidedthattheanalysisshouldrepresentspatiallydiverseearthquakesacrossarangeof

magnitudesinordertobetterunderstandearthquakeseffectsindifferentregions.Therefore,ten

earthquakesofvaryingmagnitudes,indifferentregionswereselected.

Thestudyalsolookedatotherfactorsthataffectthedamagedonebyearthquakes,such

asdevelopmentandGDPinrelationtopopulation.OnArcmap,twochoroplethmapsweremade

toshowcontrastbetweencountries'GDPandpopulation.Thiswasdonebysymbolizationof

GDPandpopulationthroughgraduatedcolors.

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Results

Figure1

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AnalysisofPopulationandGDPinRelationtoEarthquakeDamage

Aglobaleconomicandpopulationassessmentwascompletedusinggraduatedcolorsina

chloroplethmap.Thismapinformedthepotentialforearthquakedamageindifferentcountries.

Activeearthquakeregionswithhighpopulationsareofinterestbecausetherewilllikelybea

highnumberofpeopleaffectedthroughinjuryandevendeath.Placeswithnoteworthy

populationsaretheUnitedStates,Brazil,Nigeria,China,Japan,andRussia.

GDPisanotherpotentialindicatorofdamagedone.Althoughnationalincomeplayslittle

roleinexplainingwhichnationsarelikelytoexperienceanaturaldisaster,poornationsare

likelytohavepoorlyconstructedbuildingsandinfrastructurethatcouldcollapseduringan

earthquake,whilerichnationsarelikelytohaveexpensiveinfrastructurethatwillbemore

sturdyinanearthquake,buthaveahighreplacementcostifdamaged.(Kahn,2005).Placeswith

thelowestGDPareMongolia,mostofAfrica,andWesternSouthAmerica.Placeswithhighest

GDParetheUnitedStates,WesternEurope,India,China,Japan,andRussia.Thelocationsof

interestforlargeearthquakesandtheirrelateddamagearehighlypopulatedareaswithextreme

incomequalitiessuchasverywealthyorverypoor.

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Figure2

AnalysisofRichterandMercalliScales

ThepurposeofthisresearchistocomparetheRichterandMercalliscalesfortheir

accuracyinrepresentingdamagedonebyearthquakes.Inordertopursuethisanalysis,itis

importanttounderstandthedifferencebetweenthesescales.TheRichterscaleisusedtoratethe

magnitudeofanearthquaketheamountofenergyitreleased.Thisiscalculatedusing

informationgatheredbyaseismograph.TheRichterscaleislogarithmic,meaningthat

wholenumberjumpsindicateatenfoldincreaseinenergyreleased.Theintensityscaleby

Mercallimeasurestheeffectsoftheearthquakeonpeopleandbuildingsintheaffectedarea.Itis

uniquefromtheRichterscalebecauseitincorporatesobservationsbypeopleandissubjective.

Affectedpeopleareaskediftheywereawakenedbytheearthquake,iffurnituremoved,was

theredamagetochimneysortowallsintheirhome.Engineersalsoexaminestructuraldamageto

buildingsandothermanmadestructures.Thisinformationiscompiledtocreateanintensity

map.ThemaphascirclesradiatingoutfromtheepicenteroftheearthquakewithRoman

numeralsshowingtheintensityoftheearthquakeindifferentareas.Thesetwoscaleshave

entirelydifferenttechniquesformeasurement,butthequestionstillremains,whichdoesabetter

jobrepresentingtheactualeffectsofanearthquake?

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TheearthquakesofinterestforthisstudyarethosewhichtheRichterandMercalliscale

isindisagreementofeachotherandarelocatedwithinthepreviouslydescribedregionsof

interest.ThismapisgivenagraduatedcolorscalefordevelopmentasasupplementfortheGDP

datatohelpwithanalysis.Development,GDP,andearthquakedamagearecloselycorrelated,a

10%increaseinpercapitaGDPdecreasesnationalearthquakedeathsby5.3%(Kahn,2005).

ThemeasurementforeachearthquakescaleisrepresentedinFigure2bythecoloreddots.

EarthquakesthatsatisfythecriteriaforstudyareintheUnitedStates,Chile,India,China,and

Japan.Acloserlookateachoftheseearthquakeswillshedlightonwhyadiscrepancyexists

betweenthescales.

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Figure3AnalysisofChinaandJapan

Figure3showsbotheconomydevelopmentcategorizationandaMercalliIndexratingofthree

earthquakes.Higherresolutionpopulationdatahasbeenoverlayed,withdarkershadesrepresenting

higherpopulationandlightershades,lowerpopulation.Chinaisconsideredalevel3worldemerging

economyfromthepreviousmapondevelopment.Historically,Chinaisnotableforitsmembershipin

thetopfiveglobalemergingeconomiesknownasBRICS(Mishra,2014).BRICScountriesinclude

Brazil,Russia,India,China,andrecentlyaddedSouthAfrica.Theyaredistinguishedbytheirlarge,

fastgrowingeconomiesandsignificantinfluenceonregionalandglobalaffairs.Withinthiscontext,

manyoncesmallvillageshavetransformedintolargetownsandevenmegacitiesincorrelationwiththe

growthoftheeconomy.However,thisrapidgrowthisoftenattheexpenseofproperconstructionand

buildingcoderegulationforhazardssuchasearthquakes,especiallyinChina(Gurria,2013).In

earthquakeproneregionsontheeastcoastofChina,withconcentratedpopulationandpoorbuilding

coderegulation,disasterisinevitable.

Figure3showsthelocationandMMIofthreeseparateearthquakes,locatedinChinaand

Japan.TheearthquakeinChinashowninFigure3isrepresentedbyareddotwithanMMIof11.This

isthesecondhighestpossibleleveloftheMercalliscale.Itwasgivenamagnitudeof7.5ontheRichter

scale,whichisstrong,butbarelywithintheclassificationabovewhicharelikelytocausestructural

damage(magnitude7andabove).LocatednearBeijingtheworlds12thlargestmegacitywithover17

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millionpeople,anearthquakeofreasonablesizeinthisregionislikelytocausenumerousinjuries,

deaths,andmillionsofdollarsindamagetoinfrastructurenottomentionlastingissueslikewaterline

disruption,highwaydestruction,powerplantmalfunctions,communicationoutages,andfoodtransport

interruptions.Thisearthquake,barelyofreasonablesizeaccordingtotheRichterscale,caused

250,000deaths,800,000injuries,and5,600millionUSDindamage.Thisiswellrepresentedbythe

extremelyhighMMIclassification,butunderrepresentedbytheRichterscalemagnitude7.5.

TheearthquakeonFigure3locatedinJapanandisalsoindicatedbyareddotand11MMI.It

wasmeasuredat6.9ontheRichterscale,justshytherangefordamagetobeexpected.This

discrepancyinthemeasurementsisduetotheoccurrenceofanassociatedtsunami,populationdensity,

veryhighdevelopment,andhighGDPofJapan.TheearthquakeoccurredinJanuaryof1995,andit

costJapan100,000millionUSDindamagethemostexpensiveearthquakeofthetenexaminedinthis

report(Malone,2002).Over5,000peoplediedinthisearthquakeeventandintheaftermath,whichis

unusualforitsrelativelylowmagnitude(Malone,2012).Generally,thedatasuggeststhatwealthier

nationsexperiencehigherdamagecosts,butfewerdeaths.DuetoJapansuniquevulnerability,ithad

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extremelyhighdeathsandcosts.Theimagebelowshowssomedamagefromthisearthquake.

Figure4

AnalysisofSouthAmerica

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TheearthquakeinAntofagasta,Chileshowninfigure4,occurredintheSummerof1995,

measuringan8ontheRichteranda7ontheMercalliIndex.Thisdiscrepancyofscalesis

notablehere.Thisisaveryhighmagnitudewithalowermercallirating.Thecityishighly

populatedwithoneofthehighestGDPsofthecountry(Llera,1995).Theanswerliesinthe

historyandgeologyoftheregion.UnusuallyheavyrainsoccurredinAntofagastainJune1991,

whichduetoitsextremelyaridconditions,devastatedmuchofthecitywithlandslidesand

flooding.Dozensofdeathsandthousandsofhomesandbuildingsweredestroyed,thedamage

costapproximately70millionUSD(Llera,1995).Justafewyearslater,whenthecitywasstill

inrecoveryfromtherainsof1991,thisearthquakehitacitywithlessbuildingstodestroy.The

geologyofAntofagastaconverselyhelpedreducethedamageofthisnaturaldisaster.Insome

areasoftheworld,severeearthquakedamageistheresultofliquefactionofsoil.Intheright

conditions,theviolentshakingfromanearthquakewillmakelooselypackedsedimentsandsoil

behavelikealiquid.Whenabuildingorhouseisbuiltonthistypeofsediment,liquefactionwill

causethestructuretocollapsemoreeasily.Highlydevelopedareasbuiltonlooseground

materialcansufferseveredamagefromevenarelativelymildearthquake.Fortunately,

Antofagastaisinoneofthemostaridplacesintheworld,andthehard,drysoilmadeitdifficult

fortheearthquakewavestotravel.Thisdataandhistoryshowthatthemagnitudeofenergy

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released,asmeasuredbytheRichterscale,doesnotgiveacompleterepresentationoftheactual

shakinganddamagedonebyanearthquake.

Figure5

AnalysisofCalifornia

The1994Northridge,CaliforniaearthquakeshowninFigure6wasmeasuredata6.7(notinthe

usualdamagecausingrange)ontheRichterscaleanda9ontheMercalliIndex.These

measurementsareinpartialagreement,howevertheMercalliappearedtounderrepresentthe

damageandintensitywhichoccurred.Thenumberofdeathswasrelativelylowat60,butthere

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was40,000millionUSDinstructuraldamagesecondonlytoJapanscostsinthisstudy

(Malone,2002).Incontextoftheregionsdemographics,theUnitedStatesisinthehighestGDP

level,highestdevelopmentlevel,andsecondhighestpopulationlevel.Thissetofeconomic

circumstancesissimilartothe1995Japanearthquake,themaindifferenceswereaslightlylower

magnitudeandthatthecityaffectedinCaliforniawasnotasdenselypopulatedasthecityin

Japan,whichislikelythereasonforthequitelowdeathtollintheNorthridgeearthquake.The

MercalliIndexwouldbetterrepresentthedamageata10,primarilybecauseofthehighdamage

costs.Inthecaseofthe1994Northridgeearthquake,neitherscalegaveanaccuratedescription

ofthedamageandintensitythatoccurred.

Figure6

ScatterPlotofMagnitudeandMMI

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Asafinalconfirmationoftheanalysisinthisreport,ascatterplotofthetenearthquakeswas

generated.Scatterplotsshowthestrengthofrelationshipindatasetsvisuallyandareoftenseen

asthefinalwordonwhetherarelationshipexistsbetweendata.Asshowninfigure6,a

correlationdoesappeartoexistbetweenthetwoscales,buttherearetwonotableoutliers.The

upperleftdotat8and7isanoutlier.Thisdotrepresentsthe1995Chileearthquake,onewith

unusuallylowdamageforsuchahighmagnitudeevent.Reasonsforthisinconsistencywere

discussedatlengthintheanalysis,withtheprimaryreasonbeingthefortunategeologyofthe

region.Thedotat7and11istheothernotableoutlier,whichisthe1995Japanearthquake.The

mainreasonsforthisdisconnectisthedangerousmixofrisksinJapanwhichmakeitvulnerable

tonaturaldisastersingeneral.Ultimately,thetwoscalesareinagreementmostofthetime,with

afewoutliersfavoringMercalliasthebestindicatorforactualdamageandlossoflifecausedby

anearthquake.Evenwiththeissueofsubjectivityfromthepublicsinputforitsdata,itisstilla

betterindicatorofdamagethantheRichterScale..

Conclusion

ThestudysanalysisshowsthattheMercalliIndexisabetterrepresentationofdamage

donetonearbycitiesovertheRichterscale,despiteitssubjectivity.Wealsofoundthat

earthquakesinnationswithmoredisasterpreparednessdidnotharmonizetherelationship

betweenthescales,aswehadhypothesized.

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Theearthquakesmagnitudesconveyedtheamountofenergyreleasedbytheindividual

disastersbutdoesnotgiveinsightintotheexpecteddamage.Thestudynotedthatwhilemost

highlydevelopedareasincurredhugeamountsofdamagefromearthquakes,therewasa

significantlysmallerdeathtoll.Amongthetenearthquakesexamined,Japanistheexception

withahighnumberofdeathsanddamagecost.Theanalysisshowedthatthisisduetothehigh

populationdensityanddevelopmentfoundinJapan.Asidefromoutliersliketheearthquakein

JapanthereseemstobeapositivecorrelationbetweentheMercalliindexandearthquake

magnitude.Highermagnitudeearthquakeswillleadtomoredamagebuttheamountofdamage

willalsodependonhowwelldevelopedaregionis.Countriesinwhichthereisahigherstandard

oflifecanexpectahighercostindamagesbutamuchlowerdeathcount.Toconclude,an

earthquakesmagnitudecangiveusanideaofhowmuchdamagecanbeexpected,but

consideringtheMercalliIndexisvaluablebecauseittakesotherfactorssuchaslocationand

levelofdevelopmentintoaccount.

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