AnearthquakeistheresultofasuddenreleaseofenergyintheEarth'scrustthatcreatesseismicwaves（地震波）.Earthquakesarerecordedwithaseismometer（地震检波器）,alsoknownasaseismograph（地震仪）.Themomentmagnitudeofanearthquakeisconventionallyreported,ortherelatedandmostlyobsoleteRichtermagnitude(里氏量级）,withmagnitude3orlowerearthquakesbeingmostlyimperceptible感觉不到的andmagnitude7causingseriousdamageoverlargeareas.IntensityofshakingismeasuredonthemodifiedMercalliscale（麦加利震级,麦氏震级）. 　　AttheEarth'ssurface,earthquakesmanifestthemselvesbyashakingandsometimesdisplacement（位移）oftheground.Whenalargeearthquakeepicenter（震中）islocatedoffshore,theseabedsometimessufferssufficientdisplacementtocauseatsunami（海啸）.Theshakinginearthquakescanalsotriggerlandslidesandoccasionallyvolcanicactivity. 　　Initsmostgenericsense,thewordearthquakeisusedtodescribeanyseismicevent—whetheranaturalphenomenonoraneventcausedbyhumans—thatgeneratesseismicwaves.Earthquakesarecausedmostlybyrupture（破裂,裂开）ofgeologicalfaults（断层）,butalsobyvolcanicactivity,landslides,mineblasts,andnuclearexperiments. 　　Anearthquake'spointofinitialruptureiscalleditsfocusorhypocenter.Thetermepicentermeansthepointatgroundleveldirectlyabovethis.