For use With Chapter 14
Waves and Energy Transfer
Posted August 3, 1998
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.
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.
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
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
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.
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.
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.
Visit the USGS National Earthquake Information Center site
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.
Monastersky, Richard. "Racing the Waves." Science News,
Vol. 153, 14 March 1998, pp. 169-171.
Ground Motion Map