Earthquakes occur primarily because of the sudden release of built-up stress and energy in the Earth's crust due to movements along faults or fractures. The Earth's crust is divided into tectonic plates that slowly move and interact at their boundaries. When these plates are stuck due to friction, stress accumulates until it exceeds the strength of the rocks, causing a sudden slip or break. This slip releases energy in the form of seismic waves, which cause the ground to shake, resulting in an earthquake.
How Earthquakes Happen
- Earthquakes mainly happen along faults where rocks fracture and slip past each other due to tectonic plate movements.
- The sliding or slipping does not happen smoothly but in a stick-slip manner where stress builds up and then releases suddenly.
- This release of energy sends shock waves through the surrounding rock, causing shaking at the surface.
Causes of Stress Build-up
- The tectonic plates move slowly over the semi-fluid mantle beneath them.
- Forces at plate boundaries—such as collision, pulling apart, or sliding past each other—generate stress.
- These stresses deform rocks until they fracture suddenly, releasing the stored elastic strain energy.
Resulting Phenomenon
- The sudden release of stress causes seismic waves (both body waves traveling through Earth’s interior and surface waves traveling along the surface) which we experience as shaking during an earthquake.
- The location underground where the rock first breaks is called the focus or hypocenter; the point on the surface above it is the epicenter.
In summary, earthquakes occur due to the sudden slip on faults caused by the accumulated stress from tectonic plate movements, releasing energy as seismic waves that shake the ground.
