What is an earthquake?

Earthquakes are the most deadly serious natural hazards in the world and usually cause substantial damage. They correspond to a superficial or deep crack in resistant rocks. When the crack forms, energy is released as elastic waves which spread inside the ground, and the ground vibrates.

Earthquakes, just like volcanos and mountain ranges, are not spreaded randomly all over Earth. They spread along zones where the globe's elements meet : the lithospheric plates. The lithosphere is the Earth's outer layer. It is made up of plates considered to be rigid solids moving at the surface of the Earth. The plates' borders are the zones where the lithosphere becomes deformable, and this is therefore characterized by high seismic activity.