Why does the world have Earthquakes?
Well, the most basic I can give you is that the world has giant continental plates underneath the surface of the earth and these plates shift and move because of a multitude of things, there could be a a pressure rise or release underneath or beside them because of the convection cycle of molten rock in the center of the earth, or another plate could run into one plate and cause a chain reaction. In any case, when these plates shift underneath us we feel earthquakes. We dont necessarily feel every one though, most are actually untraceable.