Earth's Crust in Motion
Earthquakes
• So….
• What is an Earthquake?
• And…
• What are some things
that can cause them?
Stress in the Crust
1. An earthquake is the shaking that
results from the movement of
rock beneath Earth's surface.
– This is a super powerful force!!!
– These forces are examples of
stress.
2. Stress is a force that acts on rock
to change its shape or volume.
Types of Stress
3. There are three different kinds of stress
that occur in the Earth’s crust…
– Shearing
– Tension
– Compression
• All of this stress works over millions of years to
change the shape of rock.
4. So…Any change in the shape of Earth's
crust is called deformation.
Shearing
5. Stress that pushes a mass of rock in two
opposite directions is called shearing.
• Shearing can cause two slabs of rock to slip
past each other like the picture below.
• What feature in California is an example of this?
Tension
6. Tension is a stress that pulls on the crust,
stretching rock so that it becomes thinner in
the middle.
• Tension occurs where two plates are moving apart.
• Think of pulling a Milky Way candy bar apart.
• What ocean feature is this an example of?
Compression
7. Compression is a stress force that
squeezes rock until it folds or breaks.
• One plate pushing against another plate
can compress rock easily….
• Almost like Mr. Wise’s strength!!!
Kinds of Faults
• When enough stress builds up in rock, the rock
can break, creating a fault.
8. A fault is a break in the crust where two
slabs of crust slip past each other.
• The rocks on both sides of a fault can either
move up or down or sideways.
• Faults usually occur along plate boundaries
9. There are three main types of faults:
• Strike-slip faults
• Normal faults
• Reverse faults
Strike-Slip Faults
10. Shearing creates strike-slip faults.
11. In a strike-slip fault, the rocks on either side of the
fault slip past each other sideways
• A strike-slip fault that forms the boundary between two
plates is called a transform boundary.
• What fault in California is an example of this?
Normal Faults
12. Tension forces in Earth's crust
cause normal faults.
13. In a normal fault, the fault is at an
angle, so one block of rock lies
above the fault while the other
block lies below the fault.
• Tension forces create normal faults
where plates diverge, or pull apart.
• What ocean feature is an example of
this?
Normal Faults
Reverse Faults
14.Compression forces
produce reverse faults.
15. A reverse fault has the
same structure as a normal
fault, but the blocks move
in the opposite direction.
• What geologic feature is an example
created by compression?
Reverse Faults
Mountain Building
• The forces of plate movement can build up Earth's surface.
• Over millions of years, fault movement can change a flat
plain into a towering mountain range
Mountains Formed by Faulting
16.When normal faults uplift a block
of rock, a fault-block mountain
forms.
Mountains Formed by Folding
• Under certain conditions, plate movement can
cause crust to fold.
17.Folds are bends in rock that form when
compression shortens and thickens part of
Earth's crust.
• The collisions of two plates can cause
compression and folding of the crust.
• Some of the world's largest mountain ranges,
such as the Himalayas and the Alps, formed
when pieces of the crust folded during the
collision of two plates.
• Such plate collisions also lead to earthquakes!
Mountains Formed by Folding
Anticlines and Synclines
18. A fold in rock that bends upward into an arch is an
anticline.
19. A fold in rock that bends downward in the middle to form
a bowl is a syncline.
• Anticlines and synclines are found on many parts of Earth's
surface where compression forces have folded the crust.