When we look at the Earth, it appears to have a smooth, unified surface. However, the surface (outermost layer of the crust and upper mantle) is actually made up of many large, flat pieces of rock called tectonic plates.
The plate tectonic theory tells us that the Earth's rigid, outer shell (lithosphere) is broken into a mosaic of plates that can slide over the uppermost layer of the mantle. The plates are in constant motion, moving at a rate of 2 to 12cm per year. Heat cycles in the fluid layer beneath the Earth's crust create convection currents that lead to the constant motion of the tectonic plates. There are three common plate boundaries: convergent (plates crash together), divergent (plates move apart) and transform (plates slide past each other).
In some areas where the plates contact each other, the motion of plates isn’t smooth—some parts of plates get stuck against each other while other parts keep moving. When the stress and strain becomes too great, rocks break and the plates move suddenly. This sudden movement accompanied by shaking is known as an earthquake. Read on...
Check out these fun, hands-on earthquake demos, games and activities.
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