How do earthquakes form?
Stress in the earth's outer layer cause a pushing effect against the sides of the fault. Due to this motion, rocks slip or collide against each other releasing energy. This released energy travels in waves through the earth's crust and causes the shaking that we feel during an earthquake.
Under the surface of the earth, the two sides of a fault are constantly moving, relative to one another. This movement is known as a fault slip. The movement of these two sides is not smooth and is accompanied by a gradual build-up of elastic strain energy within the rocks along the fault.
Eventually, the strain along the fault becomes too much.The fault then ruptures with a sudden movement releasing all the energy it has built up. This energy is released in the form of vibrations called 'seismic waves'.
These waves travel along the surface and through the earth at varying speeds depending on the material through which they move. It is actually these seismic waves that cause most of the destructive effects, which we associate with earthquakes.
The location on a fault where the slip first occurs is called the hypocentre, whereas the position directly above it on the ground surface is called the epicentre.
When these seismic waves reach the surface of the earth, they give rise to strong ground motion causing building and other man-made structures to shake or collapse or develop cracks and fissures.
Earthquakes can also cause landslides, sudden eruptions as in the case of a hot lava flow from a volcano or giant waves called tsunamis. Sometimes new land mass are also formed.