Download Earthquakes

EARTHQUAKES
FAULTS
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As we learned in the previous chapter, the Earth's
plates interact with each other at plate boundaries.
The places where the plates interact are called
faults.
Watch the different fault actions
http://www.pbs.org/wnet/savageearth/animations
/index.html
•An earthquake begins when the earth around a fault
slips suddenly, releasing an enormous amount of
energy.
•The place where the slip occurs is called the focus. This is where all the
energy in an earthquake is released. The surface of the Earth directly
above the focus is called the epicenter.
Waves of Destruction
How does an earthquake damage the land? With waves of
energy. On the Origins page you learn where the energy of an
earthquake is released. That energy quickly travels away from
the focus in all directions. Look below to examine three of these
waves and how they shake the land.
1. P-Wave
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Also known as the primary wave, a p-wave is the
fastest of all the earthquake waves. Since they are
the fastest, p-waves are the first waves to be felt in
an earthquake. As these waves travel through the
Earth's crust, they shake the ground horizontally.
Click here to see a p-wave in action: PBS.org
2. S-Wave
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Also reffered to as the secondary wave, s-waves
arrive after the p-waves. They shake the earth up
and down as well as side to side.
Click here to see an s-wave in action: PBS.org
3. Surface Wave
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Sometimes reffered to as a Raliegh wave. These
waves are the slowest, but they cause the most
destruction in an earthquake. These waves shake the
earth in a rolling motion, much like at wave in the
ocean.
Click here to see a surface wave in action: PBS.org
SEISMOGRAPH
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When an earthquake occurs, scientists use a device called a
seismograph to record the waves of energy released in the
quake. A seismograph can determine what kinds of waves
were produced, and how strong those waves are.
Scientists take the results from a seismograph and compare it
to the Richter Scale. Using the scale, scientists can assign the
earthquake a number for how strong it was.
Click here to see how earthquakes measure up: GEO.MTU.edu