Transcript Earthquakes - Wayne State University

Earthquakes
An Earthquake is…
the shaking and
trembling that results
from the movement of
rock beneath Earth's
surface
The movement of
Earth's plates produces
strong forces that
squeeze or pull the rock
in the crust
Stress
• Force that acts on rock to change
its shape & volume
• Adds energy to rock until it breaks
or changes shape
• Causes deformation
• Rocks can break…creating a fault
• Causes earthquakes
Stress
There are three
different types of
stress that occur on
the crust, shearing,
tension, and
compression
These forces cause
some rocks to become
fragile and they snap
Some other rocks tend
to bend slowly like
road tar softened by
the suns heat
Shearing
• Pushes rocks in opposite
directions
Tension
• Pulls, stretching rock so it
becomes thinner in the middle
• 2 plates move apart
Compression
• Squeezes rocks until it folds or
breaks
Faults
A fault is a break in the crust
where slabs of crust slip past
each other. The rocks on
both sides of a fault can
move up or down or sideways
When enough stress builds on
a rock, the rock shatters,
creating faults
Faults usually occur along
plate boundaries, where the
forces of plate motion
compress, pull, or shear the
crust too much so the crust
smashes
Strike-Slip Faults
Shearing creates
this fault
Rocks on both sides
of the fault slide
past each other
sideways
Forms transform
boundary
Strike-Slip Faults
Normal Faults
Tension forces in Earth's
crust causes these types of
faults
Normal faults are at an
angle, so one piece of rock is
above the fault, while the
other is below the fault
The above rock is called the
hanging wall, and the one
below is called the footwall
When movement affects
along a normal fault, the
hanging wall slips downward
Occurs at divergent
boundaries
Normal Faults
Reverse Faults
Compression forces
produce this fault
Same structure as a
normal fault, but
blocks move in
opposite directions
Hanging wall slides up
over footwall
Occurs at convergent
boundaries
Reverse Faults
Friction
• Force that opposes the motion of one
surface across another
• Low friction: rocks slide without
sticking
• Medium friction: sides of the fault jam
together & then jerk-free to produce
small earthquakes
• High friction: rocks lock & don’t move,
stress increases until it overcomes
friction, produces major earthquakes
How Do Mountains Form?
1.) By Faulting- when
two normal faults
form parallel to each
other, a block of rock
in between them
moves upward as
hanging wall slips
down (fault-block
mountain)
How Do Mountains Form?
2.) Folding: when 2
plates collide,
compression forces
cause the rock to
fold or bend
Anticlines and Synclines
An anticline is a fold
in a rock that arcs
upward
A syncline is a fold
in a rock that arcs
downward
These folds in rocks
are found on many
parts of the earths
surface where
compression forces
have folded the
crust
Anticline
Syncline
Plateaus
The forces that
elevate mountains
can also raise
plateaus, a large
area of flat land
elevated high above
sea level
How Earthquakes Form