Earthquakes

Faults & Stress

Write everything in BLUE!

What are Earthquakes?

• The shaking or trembling caused by the sudden release of energy beneath Earth’s surface.

• Usually associated with faulting or breaking of rocks

• Continuing adjustment of position results in what is known as aftershocks

What is stress?

The force that acts on rock to change its shape

3 Types of stressShearingTensionCompression

Shearing: stress that pushes rock in opposite directions.

Causes masses of rock to slip past each other.

Tension

• Stress that stretches rock so it becomes thin in the middle.– Causes valleys

Compression

• Stress that squeezes rock until it folds or breaks.

• Causes hills

Questions

• What is the relationship between compression and a convergent boundary?

Questions

• What is the relationship between compression and a convergent boundary?– Both compression and convergent boundary

squeezes rocks together to form mountains or hills.

How is energy stored in Rocks?

– Rocks are put under stress so they become deformed or bend.

– Once the strength of the rock is exceeded rupture occurs and the rocks quickly rebound to an undeformed shape

– Energy is released in waves that radiate outward from the fault

A break in the Earth’s crust is called a Fault

• 3 types of faults

Strike-Slip Fault

• There is little up or down motion

• A strike-slip fault that forms the boundary between two plates is called a transform boundary.

• Shearing stress causes strike-slip faults

Strike-Slip Fault Example

Normal Fault

• The hanging wall slips downward below the footwall.

• The Normal Fault that forms the boundary between two plates is called a divergent boundary.

Normal Fault Example:Rio Grande Rift Valley

Reverse Fault

• The hanging wall slides up and over the footwall.

• The reverse fault that forms the boundary between two plates is called a convergent boundary.

Reverse Fault Example: Appalachian Mountains (East Coast)

Questions

• Explain the difference between a normal and reverse fault

Questions

• Explain the difference between a normal and reverse fault– A reverse fault is formed at a convergent

boundary and creates mountains. A normal fault is formed with divergent boundaries and forms valleys

Worst Earthquakes in the US

• New Madrid fault on the Mississippi River in 1811

• 8.1 Magnitude• Epicenter in northern

Arkansas• 35% chance of another

major earthquake in the next 50 years

New Madrid, MO