Like we mentioned before our earth is an amazing place! There are so many mysteries hidden beneath our feet. One of those mysteries is that of the drifting or moving crust. You see the earth's crust is actually made up of plates that float like rafts on the water. These plates are often moved when heat rising from below the crust pushes them from place to place.
Sometimes these plates will collide or grind together. When they collide they may often buckle producing mountains. In fact, most of our earth's ranges are found near plate edges. These plates are responsible for the trenches and mountains that are found in the oceans. When plates move apart, they create a gap. The gap will sometimes fill with molten lava, but it will still leave a deep crack. These cracks are the immensely deep ocean trenches.
What do you think happens when the plates grind against each other? They produce earthquakes. The rough edges grind against each other and then sometimes stop. Yet, the pressure to move is still there. When the rocks finally give in they crack, the plates jump ahead and move. This is what causes an earthquake to happen. Sometimes the rocks will just bend without moving - and that is called a fold. Other times, the rocks will just crack without moving and that is called a fracture.
Earthquakes can be measured by their magnitude on a Richter scale. About 80% of earthquakes occur within a the circum-pacific belt. This is the edge of the plate that circles the Pacific Ocean.