Earthquake Facts: Why do Earthquakes Happen?

An earthquake occurs when there is a sudden release of energy in the Earth’s crust that creates seismic waves. They are recorded using a seismometer, also known as a seismograph. The Richter scale is used for measuring the earthquakes.

Under the Earth's crust lies the upper part of the mantle composed of liquid rock. The plates of the Earth's crust float on top of this layer, and can be forced to shift as the upwelling molten material below moves. As the plates shift (and thus interact with each other), a huge amount of energy is released in the form of waves.

Although they can occur anywhere on the planet with little or no warning, the strongest earthquakes occur near the plate boundaries, as the plates converge (collide), diverge (move away from another), or shear (deformation/lateral cutting off the parts when they slide past each other). Moving rock and magma of a volcano can also cause an earthquake. In all of these events, large sections of the crust could get fractured and move to and fro to dissipate the released energy.

Earthquakes occur in the interior of a plate less frequently. There are different kinds of earthquakes and different kinds of faults. A strike-slip fault causes horizontal movement and shaking. Dip-slip faults create the vertical motion. In normal dip-slip faults, the earth falls inside. In a dip-slip thrust fault, the earth is pushed upwards. There are different kinds of seismic waves. Certain waves rumble the ground surface for hundreds or even more than a thousand miles. Other kinds of seismic waves travel throughout the planet. Earthquakes can also be caused by construction of large buildings and dams, injecting liquid into wells, oil drilling or any deep mining activity in general.

Undersea earthquakes can cause tsunamis. Most of the world's earthquakes take place in the 40,000-km-long, horseshoe-shaped zone called the circum-Pacific seismic belt, also known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate.