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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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