Earthquakes always have been happening on the planet earth.  With the help devices
made by man kind like bombs, buildings, and even cars have put stress amongst the
wonderful lands of earth by shaking the earth's plates and sometimes that can 
cause an earth shaking experience, or an earthquake.  Actually earthquakes happen a
lot on this wonderful planet, but most of them are not big enough for us to feel them.
Big earthquakes can happen maybe every month  years this matters on the amount of 
stress being brought upon the earth and so there are very few big earthquakes but
there still are some pretty big ones.

   The earth's crust and upper mantle are the cause of all major earthquakes.  That
is because the earth's crust can suddenly move.  Beneath the earth are 12 big plates.
they have certain boundaries.  The earth can press those boundaries very tightly 
and then they become hard to move.  Then the earths plates get stuck against each other 
and cause a lot of friction and eventually the friction will break and cause them to 
move apart and cause an earthquake.