Earthquakes!

Earthquakes!8SCIENCE Tues. April 5

What is an earthquake?

Review:• Sections of the Earth’s crust (plates) move and

cause rocks to bend and stretch • If there is enough force the rocks will break,

release energy and cause vibrations = earthquake

Where are these plates found?• These plates are made of Earth’s crust • Review layers of the Earth: animation– Crust– Mantle – Outer core– Inner core

What is an earthquake?• Earth’s crust is in constant motion because of forces

inside the earth • These cause sections of the crust (plates) to move which

puts force on the plates• 3 types of force:– Compression– Tension– Shear

Forces form faults• Compression = force that pushes together • Tension = force that pulls apart • Shear = force that moves past the other ↑↓

• These forces cause rocks to break and move along surfaces called faults

Different Forces produce Different Faults

• To see the above in motion:• When rocks are stretched they may break and

an earthquake will result• When they break, energy is released along

fault surfaces, also called an earthquake!

FORCE FAULT MOVEMENT

TENSION NORMAL Rocks move down

COMPRESSION REVERSE Rocks move up

SHEAR STRIKE – SLIP Rocks do not move up down but past each other