1. What makes the Earth shake?
Seismic Waves
What makes the Earth shake?

2. What is a seismic wave?
The waves of energy caused by the sudden breaking of rock within the earth or an explosion.
The energy that travels through the earth and is recorded on seismographs.
Types of Waves:
Primary Waves or P-Waves
Secondary Waves or S-Waves
Surface Waves or L-Waves

3. Primary Waves (P-waves)
Fastest kind of seismic wave.
Compression Wave
Move through solid rock and fluids, like water or the liquid layers of the earth.
Pushes and pulls the rock as it moves through, just like sound waves push and pull the air.

4. Compression Wave
Like a slinky.

5. Primary Waves (P-waves)

6. Secondary Waves (S-waves)
A Transverse Wave
An S wave is slower than a P wave and can only move through solid rock.
Cause rock particles to move at right angles to the direction of wave.

7. Transverse Wave

8. Secondary Waves (S-waves)

9. Surface Waves (L-waves)
When S & P waves reach the surface, their energy is converted to surface waves.
Slowest moving waves
Responsible for damage.

10. Two Types of Surface Waves

11. Locating an earthquake
Remember, S waves are slower than P waves, and seismologists use this fact to tell how far away it is from the seismograph to the earthquake.
The seismograph records the P wave first, then the S wave.
If the seismologist knows the speed of each wave, then by knowing that both waves started at the same time it’s possible to work out how far the earthquake waves have traveled to reach the seismograph.

12. Locating an earthquake

13. Locating an earthquake
If we can determine the distance of the same earthquake from at least 3 seismograph stations, we are able to locate the epicenter, the point on the Earth’s surface directly above the earthquake focus.

14. Locating an earthquake