Download Normal Fault

Normal Fault
Normal Fault
• A normal fault acts in a way similar to a
divergent boundary
• The difference between a normal fault and a
divergent boundary is when a normal fault pulls
apart, the hanging wall slides down. When a
divergent boundary pulls apart, the two plates
separate.
Under the Earth
• Convection in the earth moves the
plates, and while this is happening
stress is put onto the faults, which
makes them eventually move.
Motions Underground & Formations on
Top
• When the fault is put under enough stress,
the hanging wall slides down, making an
earthquake. Because most faults are under
water, this creates a big wave when the
fault shifts.
Focus Location and Magnitude
• The damage of an earth quake partially depends
on the depth of the focus point, or hypocenter,
within the earth.
• Earthquakes are divided into 3 categories
depending on how deep the focus point is –
shallow-focus (within 60 kilometers),
intermediate focus (60-150 kilometers), and
deep-focus (150+ kilometers)
• Since Earth’s lithosphere is typically only that
deep on continents, deep-focus earth quakes
occur on land or close to shore.
Focus & Rock Composition
• Even if a weak earthquake has a shallow hypocenter,
it may cause a lot of damage because of the short
distance that it has to travel to reach the surface.
There isn’t a lot of crust above it to vibrate, so they
are still strong.
• The deeper the hypocenter is, the more material on
top needs to be vibrated by the energy from the
earthquake, so it reduces the damage on earth’s
surface.
• The mass of the surrounding material is important,
too. For example, if the crust between the focus and
the surface is mainly composed of a material like
granite, the impact won’t be as bad compared to if it
is a lighter material, like limestone.
Time and Magnitude
• The plates shift about two inches per year. The
longer that the plate can’t move it’s two inches
every year, the more stress is built up. Once the
plate, or fault, finally shifts, there will be more
movement. The longer that the plate is stuck will
give the earthquake a greater magnitude.