EveryonehasheardoftheSanAndreasfault（断层）,whichconstantlythreatensCaliforniaandtheWestCoastwithearthquakes.ButhowmanypeopleknowabouttheequallyseriousNewMadridfaultinMissouri?
BetweenDecemberof1811andFebruaryof1812,threemajorearthquakesoccurred,allcenteredaroundthetownofNewMadrid,Missouri,ontheMississippiRiver.Propertydamagewassevere.Buildingsintheareawerealmostdestroyed.Wholeforestsfellatonce,andhugecracksopenedintheground, releasingsomestrongsmellchemicals.
TheMississippiRiveritselfcompletelychangedcharacter,developingsuddenrapidsandwhirlpools(激流和漩涡).Severaltimesitchangeditscourse,andonce,accordingtosomeobservers,itactuallyappearedtorunbackwards.FewpeoplewerekilledintheNewMaridearthquakes,probablysimplybecausefewpeoplelivedintheareain1811;buttheseverityoftheearthquakesareshownbythefactthattheshockwavesrangbellsinchurchtowersinCharleston,SouthCarolina,onthecoast.BuildingsshookinNewYorkCity,andclockswerestoppedinWashington,D.C.
ScientistsnowknowthatAmerica'stwomajorfaultsareessentiallydifferent.TheSanAndreasisahorizontalboundarybetweentwomajorlandmassesthatareslowlymovinginoppositedirections.Californiaearthquakesresultwhenthetwomassesmakeasuddenmove.
TheNewMadridfault,ontheotherhand,isaverticalfault;atsomepoints,possiblyhundredsofmillionsofyearsago,rockwaspusheduptowardthesurface,probablybyvolcanoesunderthesurface.Suddenly,thevolcanoescooledandtherockcollapsed,leavinghugecracks.Evennow,therockcontinuestosettledownwards,andsuddensinkingmotionscauseearthquakesintheregion.Thefaultitself,alargecrackinthislayerofrock,withdozensofothercracksthatsplitofffromit,extendsfromnortheastArkansasthroughMissouriandintosouthernIllinois.
ScientistswhohavestudiedtheNewMadridfaultsaytherehavebeennumeroussmallerquakesintheareasince1811;thesesmallerquakesindicatethatlargeronesareprobablycoming,butthescientistssaytheyhavenomethodofpredictingwhenalargeearthquakewilloccurThispassageismainlyabout___________TheNewMadridfaultis__________Thispassa