The same reason any earth quake happens.
The earth isn't one solid ball, it consists of parts that move against each other. Usually the movement is fairly smooth, but every now and then there'll be a hangup.
And when that hangup finally breaks free there's a jerk, and that jerk is an earth quake.
2009
fiftyfive
1964
1988
china
In the top part of the mantle and on land.
hati next new york
Port-Au-prince
January 12, 2010
Where the different tectonic plates meet
Pronouns that can take the place of the noun 'earthquake' are:it (personal pronoun)its (possessive adjective)itself (reflexive pronoun)that (relative pronoun/demonstrative pronoun)
It was a 9.3 magnitude earthquake. It was the 2nd worst earthquake that have ever recorded.