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Earthquakes

Earthquakes are caused wind energy in the Earth's crust is suddenly released, creating seismic waves. The strength of the earthquake is recorded with a seismometer. The Richter scale is a common way to report the magnitude of an earthquake. In this system, the earthquake is given a number ranging from one to nine. Earthquakes with magnitude 3 or less are barely perceptible; those with magnitude 7 or greater will cause serious damage over large areas.

On the surface, earthquakes may cause a shaking sensation. Occasionally, the ground is displaced. If the epicenter of a large earthquake is located offshore, a tsunami may result. Earthquakes can also trigger landslides and volcanic activity. (An earthquakeÕs initial rupture point is called the hypocenter or focus. The epicenter is the point at ground level directly above the focus.)

What causes earthquakes? Usually, earthquakes are caused when geological fault rupture. They can also be caused by volcanic activity or landslides which generate seismic waves. Even humans can trigger an earthquake Ð mine blasts and nuclear experiments are known to cause the earth tremble.

While the earth may seem solid, it is created of a patchwork of tectonic plates which are in constant motion. As the plates slide past each other or crash into each other, earthquakes often results. These earthquakes can also be accompanied by volcanic activity. In volcanic regions. earthquakes may serve as an early warning of an eruption.

At times, one earthquake triggers another and another. This causes an earthquake storm which may take years to end. These earthquake storms are similar to aftershocks, although with storms, later earthquakes are just as devastating as the initial quakeÕs. The recent earthquakes which affected the North Anatolian Fault in Turkey were believed to be caused this way.

Today, most earthquakes occur in the Pacific Ring of Fire (see map, below). Other plate boundaries, like that along the Himalayan mountains, also see massive earthquakes.

Earthquakes can have devastating effects. The ground shakes and rumbles, damaging buildings, roads, bridges, and more. Occasionally, the ground will rupture, splitting wide open. This will often cause breaks to electrical power lines and gas lines, a leading to fire.

Earthquakes can also cause avalanches and landslides. These are dangerous in mountainous areas. The shaking can lead to soil liquefaction, turning solid ground into liquid. Buildings and bridges built or sink into the liquid soil, causing complete devastation.

Earthquakes that occur under the sea, or that cause landslides into the ocean, can also cause a tsunami. Many lives are lost, as in the 2004 Indian Ocean earthquake.

The effects of an earthquake can be devastating. They can cause death or severe injury. The damage to roads, bridges, and buildings prevents victims from finding shelter. Basic necessities like food and water become difficult to find and prepare. Often, disease runs rampant after an earthquake.

The 1988 Spitak earthquake claimed over 25,000 lives and left 500,000-plus homeless.

Fault types

Global plate tectonic movement

The 1988 Spitak earthquake claimed over 25,000 lives and left 500,000-plus homeless.

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