What are earthquakes and what causes them?
An earthquake is a sudden, rapid shaking of the earth caused by the breaking and shifting of rock beneath the earth's surface. For hundreds of million of year, the forces of plate tectonics have shaped the earth as the huge plates that form the surface move slowly over, under, past, and away from each other. sometimes the movement is gradual. At other times, the plates are locked together, unable to release the accumulating energy as they bend or stretch. when the forces grow strong enough, the plates suddenly break free causing the ground to shake. Most earthquakes occur at the boundaries where two plates meet; however, some earthquakes occur in the middle of plates.
Aftershocks are smaller earthquakes that follow the main shock and can cause further damage to weakened buildings. Aftershocks can occur in the first hours, days, weeks, or even months after the quake. Some earthquakes are actually foreshocks that precede a larger earthquake.
Ground shaking from earthquakes can collapse buildings and bridges; disrupt gas, electric, and telephone service; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive, seismic sea waves called tsunamis. Buildings with foundations resting on unconsolidated landfill and other unstable soils are at increased risk of damage. Also, mobile homes and homes not attached to their foundations are at particular risk because they can be shaken off their foundations during an earthquake. When an earthquake occurs in a populated area, it may cause deaths and injuries and extensive property damage.
How can I protect myself in an earthquake?
Ground vibrations during an earthquake are seldom the direct cause of death or injury. Most earthquake-related injuries and deaths result from collapsing walls, flying glass, and falling objects caused by the ground shaking. It is extremely important for a person to move as little as possible to reach the place of safety he or she has identified, because most injuries occur when people try to move more than a few feet during the shaking.
Much of the damage caused by earthquakes is predictable and preventable. We must all work together in our communities to apply our knowledge to enact and enforce up-to-date building codes, retrofit older unsafe buildings, and avoid building in hazardous areas, such as those prone to landslides. We must also look for and eliminate hazards at home, where our children spend their days, and where we work. And we must learn and practice what to do if an earthquake occurs.