You wake in the darkness, unsure about what has disturbed you. Strangely the clock on your bedside table begins to rattle about as if it has a will of its own. You become aware of a strange roaring sound outside, like a jet passing overhead. The rattling grows and strengthens. Suddenly, the earth moves, bucking like a wild animal. Your room heaves; glasses crash in the kitchen; paintings fall from the walls.
             What is it? What could make the normally stable earth move like this? Throughout human history, there have been many attempts to explain earthquakes, from a disturbance created by growling demons who live beneath the earth to the movements of the giant tortoise who carries the world on his back. Over time, other ideas were proffered: perhaps these shakings were the result of great subterranean explosions or the collapse of huge underground caverns.
             These are all myths of course. Earthquakes are caused when plates move, rub, or push against each other. The earth's crust ( the outer layer of the earth ) is made up of 7 major plates and about 13 smaller ones. The plates float on molten lava, called magma. Since the plates are floating on magma, they can slowly move.
             The place where friction occurs between plates is called a fault. A fault is a crack in a plate or a place where two or more meet. An example of a fault where two plates meet is the San Andrea's fault in California, where the Pacific and North American plates meet. The plates are about 30 miles thick under land and can be 1 to 5 miles thick beneath the ocean.
             The plates move because of convection currents. Magma has currents like the ocean does, that move in a circular motion beneath the plates. When two plates are pushing against each other, they are building up tension on the fault. When the two plates finally slip, they release a great amount of energy in the form of shock waves. The vibrations make the ground move and shake, which is an earthquake.
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