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