1. 8.1 What Is an Earthquake?
epicenter
focus
fault

2. Focus, Epicenter, and Fault

3. Slippage Along a Fault

4. 8.1 What Is an Earthquake? Earthquakes
 An earthquake is the vibration of Earth produced by the rapid release of energy
 Focus and Epicenter
• Focus is the point within Earth where the earthquake starts.
• Epicenter is the location on the surface directly above the focus.
 Faults
• Faults are fractures in Earth where movement has occurred.

5. 8.1 What Is an Earthquake?
epicenter

6. Most earthquakes occur around the “Ring of Fire”.
Pacific Ocean

7. 2011 Japan Earthquake
tsunami

8. What Caused the Japan Earthquake?
Pacific Plate, an oceanic tectonic plate, moves under Japan.

9. 8.1 What Is an Earthquake? Cause of Earthquakes-Elastic Rebound Theory
• Strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake.
• Rapid release of elastic energy stored in rock causes earthquakes -

10. 8.1 What Is an Earthquake? Cause of Earthquakes
 Aftershocks and Foreshocks
• An aftershock is a small earthquake that follows the main earthquake.
• A foreshock is a small earthquake that often precedes a major earthquake.

11. Facts & Figures
San Diego, California, and Santa Barbara, California, are on opposite sides of the San Andreas fault. They are currently approximately 350 miles apart. The plates on either side of the San Andreas fault move at about the same rate as your fingernails grow, or about 1.5/yr. At this rate, San Diego will reach Santa Barbara’s current location in approximately 10 million years!
350 miles

12. Earthquake Belts Circum-Pacific Belt” Most earth quake activity
Pacific Ocean

13. Great Quakes