What are tectonic plates?

The Earth's crust is made up of about 30 huge plates that float on the semi-liquid mantle surrounding the earth's core. There are currents and movements in the mantle, so these plates move very slowly in relation to each other - about 10 cm per year on average. The floor of the Pacific Ocean is one enormous plate. Some of the plates carrying continents also carry parts of the ocean floor. The thickness of the plates varies from 8 km to 200 km.

Earthquakes are evidence of movement of the tectonic plates that carry the continents. Most of the areas where earthquakes take place are along the edges of the plates. Friction holds the plate edges together for a while, but continuing movement means that huge stresses built up. The tension is suddenly released when the plates shift sharply and this causes earthquakes. There are other causes of earthquakes, but they all involve sudden movement of the crust along a fault or crack. The energy released in an earthquake is enormous - as much as 10,000 times the power released by the world's first atomic bomb.