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1、Anearthquake(alsoknownasaquake,tremorortemblor)istheperceptibleshakingofthesurfaceoftheEarth,whichcanbeviolentenoughtodestroymajorbuildingsandkillthousandsofpeople.Theseverityoftheshakingcanrangefrombarelyfelttoviolentenoughtotosspeoplearound.Earthquakeshavedes
2、troyedwholecities.TheyresultfromthesuddenreleaseofenergyintheEarth'scrustthatcreatesseismicwaves.Theseismicity,seismismorseismicactivityofanareareferstothefrequency,typeandsizeofearthquakesexperiencedoveraperiodoftime.EarthquakesandvolcanicactivityEarthquakesof
3、tenoccurinvolcanicregionsandarecausedthere,bothbytectonicfaultsandthemovementofmagmainvolcanoes.Suchearthquakescanserveasanearlywarningofvolcaniceruptions,asduringtheMountSt.Helenseruptionof1980.[18]Earthquakeswarmscanserveasmarkersforthelocationoftheflowingmag
4、mathroughoutthevolcanoes.Theseswarmscanberecordedbyseismometersandtiltmeters(adevicethatmeasuresgroundslope)andusedassensorstopredictimminentorupcomingeruptions.Effectsofearthquakes1755copperengravingdepictingLisboninruinsandinflamesafterthe1755Lisbonearthquake
5、,whichkilledanestimated60,000people.Atsunamioverwhelmstheshipsintheharbor.Theeffectsofearthquakesinclude,butarenotlimitedto,thefollowing:ShakingandgroundruptureDamagedbuildingsinPort-au-Prince,Haiti,January2010.Shakingandgroundrupturearethemaineffectscreatedbye
6、arthquakes,principallyresultinginmoreorlessseveredamagetobuildingsandotherrigidstructures.Theseverityofthelocaleffectsdependsonthecomplexcombinationoftheearthquakemagnitude,thedistancefromtheepicenter,andthelocalgeologicalandgeomorphologicalconditions,whichmaya
7、mplifyorreducewavepropagation.Theground-shakingismeasuredbygroundacceleration.Specificlocalgeological,geomorphological,andgeostructuralfeaturescaninducehighlevelsofshakingonthegroundsurfaceevenfromlow-intensityearthquakes.Thiseffectiscalledsiteorlocalamplificat
8、ion.Itisprincipallyduetothetransferoftheseismicmotionfromharddeepsoilstosoftsuperficialsoilsandtoeffectsofseismicenergyfocalizationowingtotypicalgeometricalsettingofthedepos