Earthquake"Seismic event" redirects here. For seismic migration, see Seismic migration.Global earthquake epicenters, 19631998An earthquake (also known as a quake, tremor or temblor) is the perceptible shaking of the surface of the arth, which can be !iolent enough to "estro# $a%or buil"ings an" kill thousan"s of people& 'he se!erit# of the shaking can range fro$ barel# felt to !iolent enough to toss people aroun"& arthquakes ha!e "estro#e" whole cities& 'he# result fro$ the su""en release of energ# in the arth(s crust that creates seis$ic wa!es& 'he seismicity, seismism or seismic activity of an area refers to the frequenc#, t#pe an" si)e of earthquakes e*perience" o!er a perio" of ti$e&arthquakes are $easure" using obser!ations fro$ seis$o$eters& 'he $o$ent $agnitu"e is the $ost co$$on scale on which earthquakes larger than appro*i$atel# + are reporte" for the entire globe& 'he $ore nu$erous earthquakes s$aller than $agnitu"e + reporte" b# national seis$ological obser!atories are $easure" $ostl# on the local $agnitu"e scale, also referre" to as the ,ichter $agnitu"e scale& 'hese two scales are nu$ericall# si$ilar o!er their range of !ali"it#& -agnitu"e 3 or lower earthquakes are $ostl# al$ost i$perceptible or weak an" $agnitu"e . an" o!er potentiall# cause serious "a$age o!er larger areas, "epen"ing on their "epth& 'he largest earthquakes in historic ti$es ha!e been of $agnitu"e slightl# o!er 9, although there is no li$it to the possible $agnitu"e& 'he $ost recent large earthquake of $agnitu"e 9&/ or larger was a 9&/ $agnitu"e earthquake in 0apan in 1/11(as of -arch 1/12), an" it was the largest 0apanese earthquake since recor"s began& 3ntensit# of shaking is $easure" on the $o"ifie" -ercalli scale& 'he shallower an earthquake, the $ore "a$age to structures it causes, all else being equal&415At the arth(s surface, earthquakes $anifest the$sel!es b# shaking an" so$eti$es "isplace$ent ofthe groun"& 6hen the epicenter of a large earthquake is locate" offshore, the seabe" $a# be "isplace" sufficientl# to cause a tsuna$i& arthquakes can also trigger lan"sli"es, an" occasionall# !olcanic acti!it#&3n its $ost general sense, the wor" earthquake is use" to "escribe an# seis$ic e!ent 7 whether natural or cause" b# hu$ans 7 that generates seis$ic wa!es& arthquakes are cause" $ostl# b# rupture of geologicalfaults, but also b# other e!ents such as !olcanic acti!it#, lan"sli"es, $ine blasts,an" nuclear tests& An earthquake(s point of initial rupture is calle" its focus or h#pocenter& 'he epicenter is the point at groun" le!el "irectl# abo!e the h#pocenter&Naturally occurring earthquakes8ault t#pes'ectonic earthquakes occur an#where in the earth where there is sufficient store" elastic strain energ# to "ri!e fracture propagation along a fault plane& 'he si"es of a fault $o!e past each other s$oothl# an" aseis$icall# onl# if there are no irregularities or asperities along the fault surface that increase the frictional resistance& -ost fault surfaces "o ha!e such asperities an" this lea"s to a for$ of stick9slip beha!iour& :nce the fault has locke", continue" relati!e $otion between the plates lea"s to increasing stress an" therefore, store" strain energ# in the !olu$e aroun" the fault surface& 'his continues until the stress has risen sufficientl# to break through the asperit#, su""enl# allowing sli"ing o!er the locke" portion of the fault, releasing the store" energ#&415 'his energ# is release" as aco$bination of ra"iate" elastic strain seis$ic wa!es, frictional heating of the fault surface, an" cracking of the rock, thus causing an earthquake& 'his process of gra"ual buil"9up of strain an" stress punctuate" b# occasional su""en earthquake failure is referre" to as the elastic9reboun" theor#& 3t is esti$ate" that onl# 1/ percent or less of an earthquake(s total energ# is ra"iate" as seis$ic energ#& -ost of the earthquake(s energ# is use" to power the earthquake fracture growth or is con!erte" into heat generate" b# friction& 'herefore, earthquakes lower the arth(s a!ailable elastic potential energ# an" raise its te$perature, though these changes are negligible co$pare" to the con"ucti!e an" con!ecti!e flow of heat out fro$ the arth(s "eep interior&435Earthquake fault typesMain article: Fault (geology)'here are three $ain t#pes of fault, all of which $a# cause an interplate earthquake; nor$al, re!erse(thrust) an" strike9slip&