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Earthquake Terminology

     110321-M-#####-006 Photo by: Gunnery Sgt. Leo Salinas

  • Aftershock—An earthquake of similar or lesser intensity that fol­lows the main earthquake
  • Earthquake—A sudden slipping or movement of a portion of the earth’s crust, accompanied and followed by a series of vibrations.
  • 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 before stopping.
  • Fault—The fracture across which displacement has occurred dur­ing an earthquake. The slippage may range from less than an inch to more than 10 yards in a severe earthquake.
  • 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 30 times more energy released than the previous whole number represents. Therefore, an earthquake measuring 6.0 is about 30 times more powerful than one measuring 5.0.
  • 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. (Terminology provided by FEMA)
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