Are You Ready?
One of the most frightening and destructive phenomena of nature is a severe earthquake and its terrible after effects. An earthquake is a sudden movement of the earth, caused by the abrupt release of strain that has accumulated over a long time. For hundreds of 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 move over, under, and past each other. Sometimes, the movement is gradual. At other times, the plates are locked together, unable to release the accumulating energy. When the accumulated energy grows strong enough, the plates break free. When the earthquake occurs in a populated area, it may cause property damage, injury and even death.
Know the Terms
- Earthquake
- A sudden slipping or movement of a portion of the earth's crust, accompanied and followed by a series of vibrations.
- Aftershock
- An earthquake of similar or lesser intensity that follows the main earthquake.
- Fault
- The fracture across which displacement has occurred during an earthquake. The slippage may range from less than an inch to more than ten yards.
- Epicenter
- The place on the earth's surface directly above the point on the fault where the earthquake rupture began. Once fault slippage begins, it expands along the fault during the earthquake and can extend hundreds of miles.
- Seismic Waves
- Vibrations that travel outward from the earthquake fault at speeds of several miles per second. Although fault slippage directly under a structure can cause considerable damage, the vibrations of seismic waves cause most of the destruction during earthquakes.
- Magnitude
- The amount of energy released during an earthquake, which is computed from the amplitude of the seismic waves. A magnitude of 7.0 on the Richter Scale indicates an extremely strong earthquake. Each whole number on the scale represents an increase of about thirty times more energy released than the previous whole number. Therefore, an earthquake measuring 6.0 is about 30 times more powerful than one measuring 5.0.
