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EARTHQUAKES
Lesson 1 - Page 7

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The energy released during an earthquake causes the ground to shake. If you are close to the epicenter of an earthquake, the shaking is usually more severe than if you were farther away. This change occurs for many reasons. Most important, seismic energy dissipates as it travels through rocks, due to friction and other effects. In addition, the different types of seismic waves travel at different speeds. This means that close to the epicenter of an earthquake, all the waves arrive at about the same time, and the ground shakes very hard for a short period of time. Further from the epicenter, the fastest waves arrive ahead of the slower waves. This spreading out of energy makes the shaking less intense.

The seismic waves generated by an earthquake can be recorded and measured on a seismograph. The record produced by a seismograph is called a seismogram.

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