5.1 Earth’s Crust in Motion Notes
Questions / Notes
What is an earthquake?
Earthquake: The shaking and trembling that comes from the movement of rock
beneath Earth’s surface.
What causes earthquakes?
When the tectonic plates of Earth’s lithosphere move they cause stress on the crust.
What is stress? How does it
create earthquakes?
Stress: A force that acts on rock to change its shape or volume. Stress adds energy
to the rock.
Stress is a force; it adds energy to the rock. Stress builds up until there is enough
energy to overcome the friction, and the land shifts.
The more energy built up, the bigger the quake.
Three Types of Stress
Are there different types of
stress? What are they?
Shearing
Pushes a mass of rock in two opposite directions. Rock breaks, slips apart or
changes its shape.
Tension
Pulls on the crust, stretching rock so that it becomes thinner in the middle. It
occurs where two plates are moving apart.
Compression
Squeezes rock until it breaks. One plate pushing on another compresses rock like a
trash compactor.
What are faults? Where do
they occur?
Faults
Fault: A break in Earth’s crust where slabs of crust slip past each other. Faults
occur when enough stress builds up in rock to make it break.
Three Types of Faults
Describe and draw the three
types of Faults.
1) Strike Slip Faults
Found at transform boundaries
The rocks on either side of the fault slip past each other sideways with little up or
down motion
Ex: San Andreas Fault.
2)
Normal Faults
Found at divergent boundaries.
Tension forces in Earth’s crust cause normal faults. The fault is at an angle, so one
block of rock lies above the fault while the other block lies below the fault. There
is up and down motion.
What is the difference
between a hanging wall and
a footwall?
Hanging Wall lies above
Footwall  lies below
When movement occurs along a normal fault, the Hanging Wall slips downward.
Tension forces create normal faults where plates diverge, or pull apart.
3)
Reverse Faults.
Found at convergent boundaries
The same structure as a normal fault, but the blocks move in the opposite direction.
The rock forming the hanging rock slides UP & OVER the foot wall.
What is friction?
Friction is the force that opposes the motion of one surface as it moves across
another surface. Friction exists because surfaces are not perfectly smooth.
Rocks move along a fault depending on how much friction there is between
opposite sides of the fault.