Tectonic plates - which make up the rigid surface of the earth - attempt to move past one another as they shift across the molten magma layer beneath. Where the plates meet - in convergent zones where plates collide head-on or attempt to slide under one another, or in shear zones where they grind side-to-side - pressure builds up which can only be relieved by an earthquake.
Some major earthquakes in 2010:
March 4, 2010
A powerful 6.4-magnitude earthquake rocked southern Taiwan, terrifying residents, disrupting communications and triggering at least one large fire. Local news reports said several people were injured.
March 3, 2010
An earthquake of 5.7magnitude disrupted President Gloria Arroyo's speech on agribusiness in a school in Tuguegarao City's northern Luzon, but no major damage or casualties were reported.
February 27, 2010
At 3am on February 27, an 8.8 magnitude earthquake happened off the coast of the Maule Region of Chile. At least 700 people are thought to have died and as many as 500,000 homes were damaged.
February 26, 2010
An earthquake with a magnitude of 7 on the Richter Scale struck the Ryuku Islands off the coast of Japan. A tsunami warning was sent out but was later cancelled. There were no reported injuries.
February 26, 2010
An earthquake measuring magnitude 5.4 struck eastern Nepal on Thursday, but there were no reports of casualties.
January 12, 2010
A catastrophic 7.0 quake hit the island of Haiti, which was followed by 54 aftershocks. An estimated 230,000 people were killed in the quake, 300,000 injured. More than a million people were also made homeless.
January 9, 2010
This quake happened in the sea, 30 miles from the city of Eureka in California. The magnitude was measured as 6.5. No major injuries were reported but dozens of people suffered minor wounds.
January 3, 2010
A quake measuring 7.2 on the Richter scale hit the Solomon Islands causing a tsunami with 10ft waves to hit the island. As many as 1,000 people were left homeless on the island of Rendova after the quake.