READ: Earthquakes

Vocabulary

1. compression: Stresses that push toward each other; this causes a decrease in the space that a rock can take up.

2. confining stress: Stress from the weight of material above a buried object; this reduces volume the rock is in.

3. deformation: Strain; the change of shape that a rock undergoes when it has been altered by stresses.

4. fracture: Break in rock caused by stresses; this happens with or without the movement of material.

5. shear: Parallel stresses that move past each other in opposite directions.

6. strain: Deformation in a rock when the stress exceeds the rock's internal strength.

7. stress: Force per unit area in a rock.

8. tension: Stresses that pull material in opposite directions.

9. earthquake: Ground shaking caused by the release of energy stored in rocks.

10. elastic rebound theory: How earthquakes are generated. Stresses cause strain to build up in rocks until they can no longer bend elastically. The rocks break and cause an earthquake.

11. epicenter: Point on the Earth's surface directly above the focus of the earthquake.

12. focus: Point where rocks rupture to cause an earthquake.

13. amplitude: Height of a wave; this can be measured from a center line to the top of the crest, or to the bottom of the trough.

14. body wave: Type of seismic wave that travels through the body of a planet; body waves include primary waves and secondary waves.

15. crest: Highest point of a wave.

16. Love wave: Surface wave that has a side-to-side motion, much like a slithering snake.

17. primary wave (P-wave): Fastest type of body wave, capable of traveling through solids, liquids, and gases.

18. Rayleigh wave: Surface wave that has a rolling motion.

19. secondary wave (S-wave): Slower moving, transverse body wave that can only travel through solids.

20. surface wave: Seismic wave that travels around the ground surface; the two types are Love and Rayleigh waves.

21. trough: Lowest point of a wave.

22. wavelength: Horizontal distance between two waves, as measured from crest to crest or trough to trough.

Summary

• Stress is the force applied to an object. Stresses can be confining, compression, tension, or shear.
• Rocks under stress may show strain or deformation. Deformation can be elastic or plastic, or the rock may fracture.
• Rocks respond to stress differently under different conditions.
• A sudden release of energy stored in rocks causes an earthquake.
• The focus is where the rocks rupture. The epicenter is the point on the ground directly above the focus.
• Most earthquakes are shallow. Shallow earthquakes do the most damage.
• Body waves travel through the body of a planet. Surface waves travel along the surface.
• There are two types of body waves: P-waves travel fastest and through solids, liquids, and gases; S-waves only travel through solids.
• Surface waves are the slowest, but they do the most damage in an earthquake.

CK-12 Foundation, Earth Science. http://creativecommons.org/licenses/by-nc-sa/3.0/