EARTHQUAKES

FAULTS

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/an

imations/index.html

•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.

•An earthquake begins when the earth around a fault slips suddenly, releasing an enormous amount of energy.

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

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

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

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

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