Transcript Your stressing me OUT!

You’re stressing me
OUT!
Stress-a force that acts on rock to
change its shape or volume.
Types of Stress
There are three basic types of stress…
• 1) Tension- This stress pulls on the crust where
plates are moving apart, stretching rock to
become thin in the middle.
• 2) Compression- This stress squeezes rock
together where plates are moving toward one
another, causing them to fold or break.
• 3) Shearing- This stress pushes rock in different
directions, causing them to slip apart or change
shape.
Kinds of Faults
• Most faults occur along plate boundaries,
where the forces of plate motion push or
pull the crust so much that the crust
breaks.
• There are three main types of faults:
– Normal faults
– Reverse faults
– Strike-slip faults
Normal Fault
Hanging wall
Footwall
• The fault is at an
angle, so one block
of rock lies above
the fault while the
other block lies
below the fault.
Reverse Faults
• A reverse fault has
the same structure
as a normal fault,
but the blocks
move in the
opposite direction.
Strike-slip Faults
• In places where
plates move past
each other,
shearing creates
strike-slip faults.
That is, the rocks
on either side slip
past each other
sideways.
Folding Earth’s Crust
A fold in rock that bends upward into an arch.
A fold in rock that bends downward to form a valley.
Fault-block Mountains
As tension forces pull the crust apart, two
parallel normal faults can form a range of
fault-block mountains.
Plateau
• A large area of flat land elevated high above sea
level. A force in the Earth’s crust can push up a
large, flat block of rock.
Earthquakes
The Earth is never still.
Everyday there are several
thousand earthquakes.
That means, somewhere right now,
there is shaking and trembling
that results from the movement of
rock beneath Earth’s surface.
Did you just feel that?
Focus
The terms
• P Waves: the first to arrive. These seismic
waves compress and expand the ground like an
accordion. They can travel through solids and
liquids.
• S Waves: secondary waves. These seismic
waves vibrate from side to side as well as up
and down. They shake the ground back and
forth. They cannot move through liquids.
• Surface Waves: R Waves and Love Waves.
When some P & S waves reach the surface they
become surface waves. Love waves roll like an
ocean wave and R waves move the land side to
side.
Monitoring Earthquakes
• Seismic waves cause
the seismograph's drum
to vibrate. But the
suspended weight with
the pen attached moves
very little. Therefore, the
pen stays in place and
records the drum’s
vibrations.
Earthquake Safety
• Causes of earthquake damage include
shaking, liquefaction, aftershocks, and
tsunamis.
• The best way to protect yourself is to drop,
cover, and hold.