Earthquakes are caused by the sudden release of stored energy in the Earth's crust. This energy is stored in the form of elastic energy as rocks are deformed by tectonic forces. When the stress on a rock exceeds its strength, it can no longer resist deformation and undergoes strain.
During deformation, rocks can behave in two ways: ductile or brittle. Ductile deformation occurs when rocks bend or flow without breaking, while brittle deformation occurs when rocks fracture or break. When rocks undergo brittle deformation, the sudden release of stored elastic energy results in an earthquake.
The process of an earthquake begins with the accumulation of stress in the rocks, which can be caused by tectonic forces, volcanic activity, or human activities like mining and drilling. As the stress increases, the rocks undergo strain until they reach their breaking point, resulting in brittle failure and the release of stored elastic energy. This energy is released in the form of seismic waves, which travel through the Earth's crust and cause the ground to shake.
Friction plays an important role in the earthquake process. As rocks are deformed and strained, they rub against each other and create frictional forces that resist the movement of the rocks. These frictional forces store more elastic energy until the breaking point is reached.