Geology 101: What causes a quake?

The Earth has four major layers: the inner core, outer core, mantle and crust. The crust and the top of the mantle make up a thin skin on the Earth's surface. But this skin is not all in one piece - it is made up of many pieces like a puzzle.

Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other. These puzzle pieces are called tectonic plates, and the edges of the plates are called the plate boundaries.

The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults. Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving.

While the edges of faults are stuck together, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released.

The energy radiates outward from the fault in all directions in the form of seismic waves. The seismic waves shake the earth as they move through it, and when the waves reach the earth's surface, they shake the ground and anything on it.