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For use With Chapter 14
Waves and Energy Transfer

Catching Some Waves
Posted August 3, 1998

Earthquakes cause waves to ripple through the ground. These waves shake buildings, bridges, and other structures, sometimes reducing them to rubble and killing many people. You can't stop earthquakes from happening, and you can't predict exactly when and where they are going to happen. However, seismologists in Southern California have discovered some new ways to warn people that earthquakes are coming.

The earthquake waves that cause the most damage move through the crust at 3.7 kilometers per second. This may seem pretty fast, but they are extremely slow compared to television and radio signals that move through the air over 80 000 times faster. Some Los Angeles residents have taken advantage of the difference in these wave speeds. While watching news coverage of earthquakes and aftershocks, sometimes the seismic waves hit the television studios first. If viewers see the newscasters start to scramble and take cover, they take cover in their own homes as well. When the earthquake waves hit only seconds later, the news viewers are prepared.

California seismologists are using the difference in wave speeds to design an early warning system. Their ultimate goal is to send a signal throughout the area to alert people that earthquake waves are coming. John R. Filson of the USGS (United States Geologic Survey) points out that these few seconds of warning could truly save lives; "School children could jump under their desks. Brain surgeons could pull back their knives. Workers dealing with toxic materials could possibly hit shutoff valves."

However, such a system would only be effective if the public is properly educated. This system would only provide a few seconds of warning--just enough time for people to grab a hold of something or stand in a safe location. Filson points out "It's not the time to get in your car and drive to pick up your kids at school."

This system could also help reduce property damage. During an earthquake, power lines are tossed around. Often they crisscross and short out, resulting in power failures and fires throughout an area. An early-warning system would give power companies that few seconds they need to shut off the power and avoid this damage.

Earthquake waves are also being studied to help rescue workers. The USGS has developed "shakemaps" for rescue teams to use to find earthquake victims. These shakemaps analyze the earthquake waves and determine which areas of cities are hardest hit. To see some of these shakemaps, visit http://www-socal.wr.usgs.gov/pga.html.

Although earthquake waves can cause billions of dollars in a few seconds, it may be the very nature of these waves that allow seismologists to save lives.

Activity
Visit the USGS National Earthquake Information Center site http://wwwneic.cr.usgs.gov to find out when the last earthquake occurred in the United States and in the world. Record the date, location and the magnitude of the earthquakes. Search through the site to find the 15 largest earthquakes in the United States. Which state had the most.

References
Monastersky, Richard. "Racing the Waves." Science News, Vol. 153, 14 March 1998, pp. 169-171.

Web Sites
Ground Motion Map Information

 


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