http://pao.cnmoc.navy.mil/PAO/Educate/OceanTalk2/indexnew.htm

The sea floor is not a flat surface

Earthquake epicenters display a typically nonrandom distribution

Seismicity defines the plate boundaries

Pacific Pacific plateplate

Nazca Nazca plateplateAustralian Australian

plateplate

South South American American plateplate

North North American American plateplate

African African plateplate

Gorda Gorda plateplate

Cocos Cocos plateplate

Antarctic plateAntarctic plate

Philippine Philippine plateplate

Ind

ian

pla

teIn

dia

n p

late

Eurasian platesEurasian platesEurasian Eurasian platesplates

Caribbean Caribbean plateplate

Some major plates

The older the sea floor the farther it is from the ridge axis

0.0

9.6

20.2

33.0

40.2

47.9

56.0

68.7

83.0

118

.0

126

.513

1.7

141

.914

9.9

156

.6

180

.0

Age of the sea floor (Ma B.P.)

A convergent plate boundary, e.g., the convergence of Nazca

and South American plates