What Causes an Earthquake?
An earthquake is caused by movements that take place beneath the Earth’s surface. The outer layer (crust) of the Earth consists of huge plates of rock that shift and move. Most earthquakes occur where the plates meet, along cracks in the Earth’s surface called faults. Blocks of rock on either side of a fault push against each other.
Great strain builds up, sometimes for years. Finally, the pressure causes the blocks to suddenly move. Shock waves shake the ground for miles around. An earthquake occurs somewhere every thirty seconds.
There are about 20 plates along the surface of the earth that move continuously and slowly past each other. When the plates squeeze or stretch, huge rocks form at their edges and the rocks shift with great force, causing an earthquake.
As the plates move they put forces on themselves and each other. When the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy which moves through the Earth in the form of waves, which we feel and call an earthquake.
Earthquakes are the shaking, rolling or sudden shock of the earth’s surface. They are the Earth’s natural means of releasing stress. More than a million earthquakes rattle the world each year. Earthquakes can be felt over large areas although they usually last less than one minute. Earthquakes cannot be predicted – although scientists are working on it!