1. What is an Earthquake? 8.1

2. Earthquake The vibration of Earth produced by the rapid release of energy.

3. Focus The point within Earth where an Earthquake originates.

4. Epicenter The location on Earth’s surface directly above the focus, or origin, of an earthquake.

5. Fault A fracture in Earth along which movement has occurred.

6. Elastic rebound hypothesis The explanation stating that when rocks are deformed, they break, releasing the stored energy that results in the vibrations of an earthquake.

7. Aftershock A small earthquake that follows the main earthquake.

8. Foreshock A small earthquake that often precedes a major earthquake.

9. Key Concept What is a fault? Faults are fractures in Earth where movement has occurred.

10. Key Concept What is the cause of earthquakes? Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great forces. When the strength of the rock exceeded, it suddenly breaks, causing the vibrations of an earthquake.