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 crust (continental and oceanic) and the upper part of the mantle, 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 tectonic plates, lies the Earth’s asthenosphere. The asthenosphere behaves like a fluid over very long time scales. There are a number of competing theories that attempt to explain what drives the movement of tectonic plates.
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.
The process of ground being subjected to a growing force until it snaps or breaks is explained in a theory called the elastic rebound theory.
Tectonic plates can move relative to each in different ways. This movement gives rise to different types of plate boundaries with different properties and characteristic earthquakes.
Studying the signals from distant earthquakes has allowed scientists to determine the internal structure of the earth.
There are a number of competing theories that attempt to explain what drives the movement of tectonic plates.
Do earthquakes and volcanoes coincide?
Using pupils to act as the lithosphere, this activity explains the competing theories of what forces drive the movement of tectonic plates.
If you were at a plate tectonic margin that was very active, what might you see? What might you hear? What might you sense? What might you feel?