【阅读理解Anearthquakehappenswhentwoplatesrub(碰撞)together.Theearthplatestravelindifferentdirectionsandatdifferentspeeds.Ifoneplateisslowlyforcedunderneaththeotherpr】
阅读理解
Anearthquakehappenswhentwoplatesrub(碰撞)together.Theearthplatestravelindifferentdirectionsandatdifferentspeeds.Ifoneplateisslowlyforcedunderneaththeotherpressurebuildsupuntiltheplatesbreakapart.Thisprocesscausesthegroundtomove.Itisanearthquake.Inotherwordsearth-quakesaretheshakingoftheearth’ssurfacecausedbytheearth’srockyouterlayerasaresultoftheenergystoredwithintheearth.Thestrainwithintherocksissuddenlyreleased(释放).
Thedamageanearthquakecausesdependsonwhereitisandthetimeitishappening.Ifanunpopulatedregionisstrucktherewillbelowlossoflifeorproperty.Ifithitsalargecitytheremaybemanyinjuriesandmuchdestruction.Manyoftheareasatriskarelargelypopulatednow.Majorearthquakeshittingthoseareastodaycouldproduceterribledamage.
Actuallythereareseveralmillionsmallearth-quakeseveryyear.Largeearthquakessuchasthe1964Alaskanquakethatmeasured9.2ontheRichterscalecausemillionsofdollarsindamage.Inthelast500yearsmillionsofpeoplehavebeenkilledbyearthquakesaroundtheworld-including240000inthe1976TangShanearthquakeinChina.
A60-secondorlessearthquakecancausedevastationthatcontinuesforyearsafterthefirsttremor(小震).In1972aseriesofsevereearthquakesstruckManaguaNicaragua.Fifteenyearslaterthecitystilllookedthewayithadaweekaftertheearthquakehitbecausethecountrydidnothavethenecessarymoneytorebuildit.
Theshakingoftheearthissometimesnotthegreatestdisaster.Itisintheensuingfiresandfloodsthatoftenthegreatestdamageoccurs.Inthe1906earthquakeitwasthefirescausedafteritthatdidthemajorityofthedamage.Anearthquakecanalsodestroydamshighaboveacityorvalleyscausingfloodstosweepdownandsweepawayeverythingintheirpath.
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Whichofthefollowingisthemainideaofthefirstparagraph?