1. Seismic Waves

2. An Earthquake begins at the…  Focus: The point where the energy is released after elastic limit is reached.  Epicenter: The point on the surface of the Earth directly above the focus.

3. Earthquakes produce three types of waves with different behaviors as they travel through materials.

4. Primary (P) Waves:  Move out from the earthquake focus.  Travel the fastest of the 3 waves.  Travel twice as fast as secondary waves.  Move by causing particles in rocks to move back and forth in the same direction that the wave is traveling.  Example: slinky  Are bent and slowed when they hit the outer core.  Longitudinal wave Blue-

5. Secondary (S) Waves:  Move out from the earthquake focus.  Move slower than primary waves.  Move by causing particles in rocks to move at right angles to the direction of wave travel.  Example: rope  Cannot travel through liquids, so they are stopped by the outer core.  Transverse Wave Red-

6. Surface Waves:  Form when P and S waves reach the surface.  Slowest Waves, Most destructive  Can cause the ground to shake making rock roll and sway from side to side.  Only travel through crust

7. Seismograph:  instrument used to record the energy released by an earthquake. Recording time of wave arrival.  Produces paper sheet called a seismogram  A stationary pen traces a record of vibrations

8. Seismograph Stations  P waves arrive first  S waves arrive second  Surface waves arrive last (slowest)  3 or more seismograph stations are needed to determine the location of the epicenter.  When an epicenter is far from a location, the p wave has more time to put distance between it and the s and surface waves.

9. Finding the epicenter...  Each city determines their distance from the epicenter.  That distance is used as the radius of a circle.  After 3 cities create circles, where they intersect is the actual epicenter.

10. Because of the behavior of these different waves…  Scientists have indirect evidence for the solid inner core and liquid outer core of the Earth.  Earthquake waves travel faster through the mantle than through the crust.  So, scientists know the mantle is denser than the crust.

11. Shadow Zone Animation  http://www.earthquake.gov/learning/ animations/animation.php?flash_title =Shadow+Zone+Flash+Animation&fl ash_file=shadowzone&flash_width=2 20&flash_height=300 http://www.earthquake.gov/learning/ animations/animation.php?flash_title =Shadow+Zone+Flash+Animation&fl ash_file=shadowzone&flash_width=2 20&flash_height=300