The edges of the plates tend to pull apart or push together slowly, but with great force. Stresses in a plate increase until a portion of the crust gives way in a sudden, violent movement called an earthquake. The breaking, tearing crust forms features called faults. Geologists locate faults and determine which are active and inactive. This helps identify where the greatest earthquake potential exists.
Most faults mapped by geologists are inactive and have no earthquake potential.
An earthquake is the shaking of the crust. A quake results when the crust moves suddenly along a fault. The sudden release of stored force in the crust causes waves of energy to radiate outward from the fault. Internal waves form surface waves and the surface waves cause the shaking of the ground. Buildings in the path of waves may tilt and roll violently as the earthquake surface waves pass.