Why and where do earthquakes occur?

World Seismicity

If we look at the pattern of where earthquakes occur around the world, it is clear that most of the earthquake activity is concentrated in a number of distinct earthquake belts.

For instance, there are many earthquakes recorded around the edge of the Pacific Ocean, or in the middle of the Atlantic Ocean.

These earthquake belts provide an important clue in the development of the theory of plate tectonics.

The outer shell of the Earth, or lithosphere, is made up of a number of rigid segments called tectonic plates. These plates are continually moving at rates of a few centimetres per year (about as fast as your fingernails grow), driven by forces deep within the Earth.

Below the lithospheric plates, lies the Earth’s asthenosphere. The asthenosphere behaves like a fluid over very long time scales, allowing it to convect. Convection acts like giant conveyor belts, moving the overlying plates around.

At the boundaries between the plates, where they are moving together, apart or past each other, tremendous stresses build up, and are where most earthquakes occur.