An earthquake is a sudden, rapid shaking of the ground caused by the breaking and shifting of rock beneath the Earth's surface. This shaking can cause damage to buildings and bridges; disrupt gas, electric, and phone service; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive ocean waves (tsunamis). Buildings with foundations resting on unconsolidated landfill, old waterways, or other unstable soil are most at risk. Buildings or trailers and manufactured homes not tied to a reinforced foundation anchored to the ground are also at risk since they can be shaken off their mountings during an earthquake. All 50 states, five U.S. territories and the District of Columbia are at some risk for earthquakes. Earthquakes can occur at any time of the year.
For millions of years, the forces of plate tectonics have shaped the earth, as the huge plates that form the earth’s surface slowly move over, under and past each other. At times, the movement is gradual. At other times, the plates are fused together, unable to release accumulated energy. When the accumulated energy grows great enough, the plates break free.
When an earthquake occurs in a populated area, it may cause deaths and injuries as well as extensive property damage. Ground movement during an earthquake is seldom the direct cause of death or injury. Most earthquake-related injuries result from collapsing walls or floors, flying glass, and falling objects as a result of the ground shaking or people trying to move more than a few feet during the shaking. Much of the damage in earthquakes is predictable and preventable.
