Earthquakes are cause by the movement of tectonic plates deep below the surface of the planet. When the tectonic plates move and come in contact with each other, mountains are formed, volcanoes erupt and earthquakes occur.

When these plates move, at times their edges touch and then they get stuck. But this only stops them temporarily. They continue to try moving and this causes a build up of stress across the plate. This stress builds and builds until it breaks the edge of the plate and the pent up energy is released as shockwaves that cause earthquakes.

The shockwaves occur at the epicentre of the affected area but as they rise towards the surface, more and more of the earth's crust begins to vibrate and so earthquakes occur although places farther away from the epicentre experience less of it.

As the plates move away from each other, magma fills the space in between and is pushed upwards by the immense pressure underground. Thus leading to a volcanic eruption. So it is said that areas with volcanoes are more likely to have earthquakes than those without. This is seen in the ring of fire. The ring of fire is a large area in the basin of the Pacific ocean which is characterized by earth quakes and volcanic eruptions.

Mostly earthquakes occur at the edges of tectonic plates and scarcely occur in other places but this does not mean that they cannot occur elsewhere. Earthquakes can happen anywhere on the planet because fault lines, which are cracks in tectonic plates can occur anywhere.