What is earthquake?

Earthquakes drop pressures that cause lasting changes in the Earth's crust.

 Many of the people living in Iran had experienced an earthquake. When we feel something violent or something slow like rolling motion of the earth if we are at sleep, we will wake up or if we are at home and watching television or driving in the street when an earthquake happens, we will amaze.

What is the reason for earthquake?

Why feel of earthquakes are so different from the other? What is earthquake?

 Earhquakes cause dropping pressure and these are the Earth's natural means. While Earth's plates moving in the opposite direction of each other, a great amount pressure will impose to lithosphere. The lithosphere breaks when the pressure is great. For example imagine you have a pencil. If you give a force to both ends of it you would sea that pencil stoop. When you give enough force, the pencil would break in the middle part, and the force that you had imposed it would dropping. The action of the Earth's crust is exactly like this .When the plates move,they stress on each other and themselves. While this pressures and stresses is great enough, the crust would break. After the crust break, the pressure will decrease as energy t moves among the Earth's layers in form of waves, and earthquake happen.