AnearthquakeistheresultofasuddenreleaseofenergyintheEarth'scrustthatcreatesseismicwaves.Earthquakesarerecordedwithaseismometer,alsoknownasaseismograph.Themomentmagnitudeofanearthquakeisconventionallyreported,ortherelatedandmostlyobsoleteRichtermagnitude,withmagnitude3orlowerearthquakesbeingmostlyimperceptibleandmagnitude7causingseriousdamageoverlargeareas.IntensityofshakingismeasuredonthemodifiedMercalliscale. 　　AttheEarth'ssurface,earthquakesmanifestthemselvesbyashakingandsometimesdisplacementoftheground.Whenalargeearthquakeepicenterislocatedoffshore,theseabedsometimessufferssufficientdisplacementtocauseatsunami.Theshakinginearthquakescanalsotriggerlandslidesandoccasionallyvolcanicactivity. 　　Initsmostgenericsense,thewordearthquakeisusedtodescribeanyseismicevent—whetheranaturalphenomenonoraneventcausedbyhumans—thatgeneratesseismicwaves.Earthquakesarecausedmostlybyruptureofgeologicalfaults,hugeamountsofgasmigration,mainlymethanedeepwithintheearth,butalsobyvolcanicactivity,landslides,mineblasts,andnuclearexperiments. 　　The2008Sichuanearthquake(Chinese:四川大地震),orGreatSichuanEarthquakewhichmeasuredat8.0Ms[5]and8.3Mw[6]accordingtoPRC'sChinaSeismologicalBureau,and7.9MwaccordingtoUSGS,occurredat14:28:01.42CST(06:28:01.42UTC)on12May2008inSichuanprovinceofChina.ItwasalsoknownastheWenchuanearthquake(Chinese:汶川大地震),aftertheearthquake'sepicenterinWenchuanCountyinSichuanprovince.Theepicenterwas80kilometres(50mi)west-northwestofChengdu,thecapitalofSichuan,withadepthof19kilometres(12mi).[2]TheearthquakewasfeltasfarawayasBeijing(1,500kmaway)andShanghai(1,700kmaway),whereofficebuildingsswayedwiththetremor.[7]Theearthquakewasalsofeltinnearbycountries. 　　Officialfigures(asofMay30,12:00CST)statethat68,858areconfirmeddead,including68,007inSichuanprovince,and366,586injured,with18,618listedasmissing.[4]Theearthquakeleftabout4.8millionpeoplehomeless,[8]thoughthenumbercouldbeashighas11million.[9]ItwasthedeadliestandstrongestearthquaketohitChinasincethe1976Tangshanearthquake,whichkilledatleast240,000people.Approximately15millionpeoplelivedintheaffectedarea. 　　Theearthquakewasfollowedbytwomajoraftershocks,whichledtothecollapseof420,000morebuildings.[10]OnMay25,amajoraftershockof6.0Mwhitnortheastoftheoriginalearthquake'sepicenter,inQingchuanCounty,causingeightdeaths,927injuries,andbillionsofdollarsindamage.