These basic stresses caused by rotation and
convection are just too much for the lithosphere. It relieves its stress
by "cracking" or better known as faults. However, the movement
along the faults cause energy to be released called seismic waves. When
the waves reach the surface of the Earth it shakes, causing earthquakes.
Earthquakes are caused by the sudden movement and
fracturing of rock masses along pre-existing faults. A fault is a broken
surface within the Earth’s crust. The point on the fault at which the
displacement begins is called the focus of the earthquake. The point on
the surface of the earth directly above the focus is the epicenter.
Faults can be caused by pull apart (extensional), compressional, or slip
slide (transform) motion.