Due to the accumulated energy liberation within world come out suddenly to balance of crust, fixed. Usually caused by the movement of the fault within the crust layer on the outside of the structure of the world. Many times.
Due to the release of energy stored within the Earth's crust suddenly to balance constant. Usually caused by movement of faults within the Earth's crust on the outside of the structure of the world. Moving or changing slowly with time.
Due to the release of the energy accumulated within the out suddenly to balance the cradle is the constant. Usually caused by movement of the fault zone in the crust on the outer of the structure of the world.. always.