1. 12.1 HOW AND WHERE EARTHQUAKES OCCUR

2. C AUSES OF E ARTHQUAKES What is an Earth quake? It is the shaking of earth’s crust due to the release of E. They are caused by strain that builds up at or along lithosphere boundaries.

3. Elastic Rebound The sudden return of elastically deformed rock shape. Two blocks of crust pressed against each other at a fault do not move because friction holds them together Crust deforms when rock is stressed and can’t hold its integrity, it then fractures. When rock fractures, it separates at the weakest point and snaps back (rebounds). This causes an earthquake

4. Elastic Rebound

5. C AUSES OF E ARTHQUAKES Faults – A break in the lithosphere along which movement has occurred. Focus – The area where first movement occurs during an Earthquake. The place where rock begins to move and break. Epicenter – The area directly above the focus.

6. B ODY W AVES Body Waves – The waves that travel through the body of a medium. Two categories: P Waves S Waves

7. B ODY W AVES P Waves – Squeeze and stretch rock material in the direction of wave movement. Fastest wave: 1 st. wave to be detected In a back-and-forth motion. Moves through solids, liquids, and gas.

8. B ODY W AVES S Waves (Shear or secondary waves) – Waves that move perpendicular to the direction in which the wave is traveling. Arrives at detection sites after P waves. Creating a side to side direction. Travel only through solid material.

9. Body Waves (P waves/S waves)

10. B ODY W AVES **Note** Andrija Mohorovicic: A Croatian scientist, in 1909 discovered the increase of seismic waves below the surface of the continents. The speed at which the waves travel is dependent on the material. Less rigid, less dense material will cause slower travel of a wave and vice versa. Studying seismic waves have helped scientist locate boundaries between other internal layers of the earth.

11. S URFACE W AVES Surface waves – Waves that travel along Earth’s surface. When P and S waves reach the Earth’s surface, surface waves are produced. Rayleigh Waves Love Waves

12. S URFACE W AVES Love waves – Causes material to move side to side perpendicular to the direction of the wave.

13. S URFACE W AVES Rayleigh Waves – Causes material to move in an elliptical pattern. Like ripples in a lake.