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from Planet, December 2003
When the Earth Trembles
by Thomas Andrews
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What can tear roads apart, twist tall buildings, change a river’s path, and rock the ground beneath our feet? Earthquakes do all that and more. They are the most powerful and unpredictable events in nature. We can predict bad weather, but an earthquake strikes without warning. Even worse, there is little we can do to prepare for the disaster.
What Makes the Earth Shake and Quake
The crust of the Earth is made up of large sections called tectonic plates. The release of heat from inside the Earth makes these plates
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move constantly like conveyor belts. The worst earthquakes occur where the edge of one plate slips under the edge of another. As the plates bump and push against one another, pressure builds up on the surrounding rock. Finally the rock snaps violently and sends out shock waves that make the Earth tremble. The release of energy and heat that causes earthquakes also helped produce Earth’s atmosphere, oceans, soil, and continents.
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To measure the size of an earthquake, scientists use a scale of numbers called the Richter scale. Each unit on the scale equals a ten-times increase in the earthquake’s power. In other words, an earthquake measuring 7.0 on the Richter scale is ten times as violent as an earthquake measuring 6.0.
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Earthquakes Strike Anytime, Anywhere
No place on Earth is completely safe from earthquakes. They have happened all over the world, and they occur all the time. Thousands happen each year, and most go unnoticed. The powerful ones, though, cause more destruction more quickly than any other natural event. The violent motion of the Earth’s surface is only one effect. Quakes also bring about deadly landslides, mudslides, and tidal waves in the ocean.
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