文章Earthquake 地震的危害.doc

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1、April18,1906,California'sSanAndreasFaultsnaps,shakingSanFranciscofornearly60terrifyingseconds.Whenthetremblingstops,thedisasterisonlybeginning.Gaslinesrupture,settingoffmassivefires,some700peopledie.Mostofthecityisreducedtoruins.Thistremblingofthegroundcaus

2、edwhenmassesofrockssuddenlyshiftbelowtheEarth’ssurfaceiscalledanearthquake.Hundredsoflittleearthquakesshaketheplaneteveryday,butmostpassunnoticed.TheyusuallyoccuralongtheboundariesofthethinplatesthatcovertheEarthlikeaneggshell.DrivenbytheheatdeepwithintheEa

3、rth’score,theplatesgrindagainsteachotheralonglinescalledfaults.Whenaplate’smotionisblocked,stressbuildsup.Finallythefaultgivesway.ThereleasedenergyraisesthroughtheEarthintheformofseismicwaves.Scientistsrecordthesewavesonadevicecalledaseismograph.Thesezigzag

4、linesshowthestrengthofvariousseismicwaves.Usingtheline,scientistsgradetheearthquakesontheRichterscale.ForaquaketomeasureonenumberhigherontheRichterscale,itmustreleaseabout30timesasmuchenergyasthenumberbelowit.Everyyearabout100,000earthquakesrumblethroughthe

5、groundhardenoughforpeopletofeelthem.Ofthese,onlyabout1,000arestrongenoughtodamageproperty.Butapowerfulearthquakecanbedevastating.Onaverage,about10,000peopledieeachyearasaresultofearthquakes.ThegreatestrecordedearthquakeevertohitNorthAmericameasuredamassive9

6、.2.ThetremorstruckAlaskaonMarch28,1964.AcameraonboardashipdockedinValdezrecordedthedrainingoftheentireharborasachasmopenedupontheseafloor.ThereisnostoppingthesurfaceoftheEarthfromchangingandmoving,soengineersarefocusingonwaystocreatebetterbuildings,highways

7、andbridges,structuresthatwillremainsafeandstayinonepiecethenexttimetheEarthbeginstoshake.