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第PAGE\*MERGEFORMAT9页共NUMPAGES\*MERGEFORMAT9页 大学英语四六级快速阅读预测(3) Passage3NaturalDisastersEarthquakesWhentheEarthMovesEarthquakesarecausedbythemotionoftectonicplates—individualsectionsthatmakeuptheEarth’ssurfacelikepanelsonafootball.Immensestrainaccumulatesalongfaultlineswhereadjacentplatesmeet.Whentherockseparatingtheplatesgivesway,suddenseismicground-shakingmovementoccurs.Ofcourse,ifwewanttoknowwhyearthquakeshappen,weneedtodigalittledeeper.CentreoftheEarthTheEarthismadeupofthreemainlayers:ThecoreisatthecentreoftheEarth.Themantleisamobilesemi-moltenlayeraroundthecore.Theouter-shelloftheEarthiscalledthecrust.Scientistscallthisthelithosphere—it’sthepartwe’reonnow.Thecrustismadeupof12individualtectonicplates.Belowthesea,theycanmeasurethreetosixmiles(4km-9.6km)thickandunderlandthisincreasesto20-44miles(32km-70.8km).Belowthecrust,radiationfromtheEarth’scoreheatsthesemi-moltenmantletotemperaturesofover5000°C.Allfluidswhenheated—evenmoltenrock—areaffectedbyaprocesscalledconvection.Thatmakeshotliquidrisetodisplacecoolerliquid,creatingacurrent.Tectonicplateseffectivelyfloatonthemantle,likecroutonsinabowlofsuper-heatedsoup.Buttheseplatesandconstantlymoveduetotheconvectioncurrent.Ofcourse,theycreepalongveryslowly—roughlythesamespeedyourfingernailsgrow.Evenatthissubsnail-pace,theeffectscanbedevastating.Thecombinedannualforceofearthquakesisequalto100,000timesthepoweroftheatomicbombsthatflattenedHiroshima.Thepointwheretheseismicactivityoccursistheepicentre,wheretheearthquakeisstrongest.Butitdoesn’talwaysendthere;seismicwavestraveloutfromtheepicentre,sometimescreatingwidespreaddestructionastheypass.VolcanoesWithoutdoubt,eruptingvolcanoesarethemostawesomeandterrifyingsightsinnature.Infact,theiruntameddestructivefirepowerhasshapedandinfluencedmanyancientculturesfromPompeii,toJapan.It’sestimatedthatoneintenoftheWorld’spopulationlivewithin“dangerrange”ofvolcanoes.AccordingtotheSmithsonianInstitute,thereare1511“active”volcanoesacrosstheglobe,andmanymoredormantonesthatcouldrechar
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