1. Earthquakes and Seismic Waves

2. **Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface.

3. Parts of Earthquakes
**An earthquake is the shaking that results when rocks move inside Earth. An earthquake is caused by stress along a fault. Stress increases until the rocks break and release stored energy.

4. Focus
**Focus - The point below the surface where the rock breaks and energy is released. (This is where the earthquake occurred.)

5. Fault
**Fault - As soon as the rock breaks, there is movement along the broken surface causing a split in the surface.

6. Epicenter
**The seismic waves from an earthquake are usually strongest at the epicenter. This is the point on the surface right above the focus.

7. Earthquakes and Seismic Waves
**Earthquakes cause waves, called seismic waves, to travel through Earth. Seismic waves carry the energy released by the rocks.
There are three kinds of seismic waves: P waves, S waves, and surface waves.

9. Seismic Waves **Primary (P) waves:
Move out from the earthquakes focus, the point where energy is released
Travel the fastest of the 3 waves.
Move through solid and liquid layers of the Earth.
4. Push and pull rock creating a back-and-forth (side to side) motion in the direction the wave is moving (longitudinal wave)

10. S waves move rocks up and down, like a wave passing through a rope when you flick it.
S waves travel more slowly than P waves but do more damage.
S waves can only go through solid rock.
S Waves

11. Surface Waves
Surface waves are combined P and S waves that travel along Earth’s surface.
Surface waves are the slowest seismic waves. They also do the most damage because they make the ground roll like the ocean.

12. Review Questions
Label each drawing as S Waves or P Waves

13. ____ P wave a. shakes buildings from side to side
Type of Wave Effect
____ P wave a. shakes buildings from side to side
____ S wave b. shakes buildings violently up and down.
____ Surface wave c. causes buildings to roll like the ocean which makes them break more easily.