"Elastic Rebound" theory is the most robust theory to explain earthquake causes.

Directed horizontal forces in lithosphere are the source of deformations in rocks and earthquakes. Energy accumulation in rocks causes shaking along fractures and faults. While the release of energy, earthquake occurs.

That is why for studying seismicity of a region, active faults of the area are investigated. It is important to notice that in an earthquake whole of a fault dose not move and some part of it dose not move. These parts may rupture and cause earthquake later. Volcanic activities, collapse of caves and mines, avalanches, meteor collision with the earth and man activities cause small earthquakes. Most of the quakes have foreshock and after shock.

Elastic rebound theory

Deformation forces in the active part of the crust that cause fraction between plates produce strain. These forces deform rocks elastically and when the rocks return to their original form, faulting starts from the focal point and propagates along default plain with the velocity of 3 Km/s. the stored energy is "Elastic Strain" that releases as an earthquake.