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Earthquakes
Faults & Stress
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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 stress
Shearing
Tension
Compression
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