EARTHQUAKES

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Earthquakes are caused by the release of energy deep within the earth and are a terrifying threat to life and property across the United States.

Although the earth feels solid, it is really only partly so.

The magnitude, or energy released, of an earthquake is measured by the Richter Scale.

The earth's crust is made up of giant plates of solid material that is riding on top of a more liquid portion of the earth's mantle. The plates have been moving slowly for millions of years. These gradual movements, slower than the growth of a fingernail, have shaped the physical features of the earth, leaving scars or "faults" where they have split or come together.

A fault is a fracture in the crust of the earth along which rocks on one side have moved relative to those on the other side. It is a thin zone of crushed rock between two blocks of rock, and can be any length, from centimeters to thousands of kilometers.

Most faults are the result of repeated displacements over a long period of time. They are areas of stress that cause a crack in the rock or soil along the earth's surface. Some may extend deep underground, towards the earth's interior. Many earthquakes occur where the earth's crustal plates grind and shift along one another.

Quakes are most active in the Circum-Pacific Belt, an area stretching from the Western United States to Eastern Asia and from the Berring Sea to the deep South Pacific.

Other earthquakes occur in the middle of the plates and are caused by the geophysical factors. Such factors include, but are not limited to, identified or unidentified faults (or "crust cracks" within the earth); the level of the water table; geological formations including soil and rock deposits over geological time; or the general stability of the soil and rock in the area.

An epicenter is the point on the earth's surface directly above the point inside the earth's mantle that is the focus or the source of the earthquake.


Some information gathered from Weather.com.

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