We live on the thin crust of a layered earth. The crust of our planet is made up of large pieces, called plates, that fit together. 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.