Rapid violent shaking of the Earth’s surface caused by rapid movement of the Earth’s rocky outer layer is known as an Earthquake. Earthquakes occur when energy stored within the Earth, usually in the form of strain in rocks, is suddenly released. Elastic Rebound Theory lays down the phenomena that causes earthquakes. It is mostly related to slippage of active fault-lines in the earth’s crust.
The motion along the fault is accompanied by the gradual buildup of elastic strain energy within the rock along the fault. The rock stores this strain energy like a giant spring being slowly tightened.