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1、.Passage1EveryonehasheardoftheSanAndreasfault（断层）,whichconstantlythreatensCaliforniaandtheWestCoastwithearthquakes.ButhowmanypeopleknowabouttheequallyseriousNewMadridfaultinMissouri? BetweenDecemberof1811andFebruaryof1812,threemajorearthquakesoccurred,allcenteredaroundth
2、etownofNewMadrid,Missouri,ontheMississippiRiver.Propertydamagewassevere.Buildingsintheareawerealmostdestroyed.Wholeforestsfellatonce,andhugecracksopenedintheground,allowingsmellofsulfur（硫磺）tofilterupward. TheMississippiRiveritselfcompletelychangedcharacter,developingsudd
3、enrapidsandwhirlpools.Severaltimesitchangeditscourse,andonce,accordingtosomeobservers,itactuallyappearedtorunbackwards.FewpeoplewerekilledintheNewMaridearthquakes,probablysimplybecausefewpeoplelivedintheareain1811;buttheseverityoftheearthquakesareshownbythefactthattheshoc
4、kwavesrangbellsinchurchtowersinCharleston,SouthCarolina,onthecoast.BuildingsshookinNewYorkCity,andclockswerstoppedinWashington,D.C.ScientistsnowknowthatAmerica'stwomajorfaultsareessentiallydifferent.TheSanAndreasisahorizontalboundarybetweentwomajorlandmassesthatareslowlym
5、ovinginoppositedirections.Californiaearthquakesresultwhenthemovementofthesetwomassessuddenlylurches（倾斜）forward. TheNewMadridfault,ontheotherhand,isaverticalfault;atsomepoints,possiblyhundredsofmillionsofyearsago,rockwaspusheduptowardthesurface,probablybyvolcanoesunderthe
6、surface.Suddenly,thevolcanoescooledandtherockcollapsed,leavinghugecracks.Evennow,therockcontinuestosettledownwards,andsuddensinkingmotionstrigger（触发）earthquakesintheregion.Thefaultitself,alargecrackinthislayerofrock,withdozensofothercracksthatsplitofffromit,extendsfromnor
7、theastArkansasthroughMissouriandintosouthernlllinois. ScientistswhohavestudiedtheNewMadridfaultsaytherehavebeennumeroussmallerquakesintheareasince1811;thesesmallerquakesindicatethatlargeronesareprobablycoming,butthescientistssayhavenomethodofpredictingwhenalargeearthquak
8、ewilloccur. 1.Thispassageismainlyabout .A.theNewMadridfaultinMissouri B.thecausesoffaults
