Chapter 9Earthquakes

Forces inside Earth

• Elastic Limit – point at which rocks will remain bent or break, due to applied stresses.

• Faults – surfaces along which rocks break and move in different directions relative to the fault surface.

• Earthquake – the movement of the ground, caused by waves from energy released as rocks move along faults.

Types of FaultsNormal Fault Reverse Fault Strike-Slip Fault

Plates move apart; Tension

Plates crash into each other; Compression

Rocks move past each other; Shearing

Ex. Mid Ocean Ridge

Ex. Rocky Mountains

Ex. San Andreas Fault

Aka Divergent Boundary

Aka Convergent Boundary

Aka Transform Fault Boundary

Earthquake Information

• Focus – the point in Earth’s interior where earthquake energy is released.

• Epicenter – the point on Earth’s surface directly above an earthquake’s focus.

Seismic Waves• These are the waves of energy that move outward

from the earthquake’s focus and make the ground shake

– Primary Waves – travel through the Earth by causing particles in rocks to compress and stretch apart (back and forth) in the direction of the wave. FASTEST WAVES

– Secondary Waves - travel through the Earth by causing particles in rocks to move at right angles to the direction of the wave.

– Primary Waves – travel through the Earth by causing particles in rocks to compress and stretch apart (back and forth) in the direction of the wave. (FASTEST WAVES)

– Secondary Waves - travel through the Earth by causing particles in rocks to move at right angles to the direction of the wave.

Surface Waves• These waves are emitted from the epicenter of an

earthquake. Give particles an elliptical and back/forth motion.

• These cause buildings to collapse. These waves cause the most destruction. (SLOWEST WAVES)