Study Guide
Chapter 4
Test
Know
all of your vocabulary! Take your Vocab
Folder home to study.
What
is stress?
Answer: Stress is a force that acts on rock to change
its shape or volume.
What
works over millions of years to change the shape and volume of rock?
· Tension-the
stress force that pulls on the crust and thins rock in the middle.
· Compression-the
stress force that squeezes rock until it folds or breaks.
· Shearing-the
stress that pushes a mass of rock in two opposite directions.
What
is a fault?
Answer: A fault is a break in the rock of the crust
where rock surfaces slip past each other.
How
do faults form?
Answer: When enough stress builds up in rock, the
rock breaks, creating a fault.
Name
and describe the 3 main types of faults.
o Normal Fault-the
fault cuts through rock at an angle, so one block of rock sits over the fault,
while the other block lies under the fault.
*The
hanging wall moves down!
o Reverse
Fault-this fault has the same structure as a normal fault, but the blocks move
in the reverse direction.
*The
hanging wall moves up!
o Strike-Slip
Fault-the rocks on either side of the fault slip past each other sideways, with little up or
down motion. (transform boundary)
How
does plate movement create new landforms?
o Anticlines-a
fold in a rock that bends upward into an arch.
o Syncline-a
fold in rock that bends downward to form a V-shape.
o Folded
mountains-the collision of two plates can cause compression and folding of the
crust over a wide area. Folding produced
some of the world’s largest mountain ranges—The Himalayas in Asia AND The Alps in Europe.
o Fault-block
mountains-two plates move away from each other and tension forces create many
normal faults. As the hanging wall of
each normal fault slips downward, the block in between now stands above the
surrounding valleys, forming a fault-block mountain.
o Plateau-the
forces that raise mountains can also uplift, or raise, plateaus (large areas of
the land elevated high above sea level).
What
causes earthquakes?
Answer: The forces of plate movement produce stress
in Earth’s crust, adding energy to rock and forming faults. Eventually the
stress increases along a fault until the rock slips or breaks, causing an
earthquake.
What
are seismic waves?
Answer: Seismic waves are vibrations that are similar
to sound waves. They travel through
Earth carrying energy released by an earthquake.
What
is the focus?
Answer: The focus is the area beneath Earth’s
surface where rock that was under stress begins to break or move. This action triggers the earthquake.
What
is the epicenter?
Answer: The point on the surface directly above the
focus is the epicenter.
Types
of seismic waves:
1)
P
Waves—The first waves to arrive are primary waves, or P Waves. These waves compress and expand the ground
like an accordion.
2)
S
Waves—The secondary waves that come after the P Waves are S Waves. These waves vibrate from side-to-side or up
and down.
3)
Surface
Waves—When P Waves and S Waves reach the surface, some of them become Surface
Waves. These move more slowly that P and
S Waves, but they can produce severe ground movements.
How
are earthquakes measured?
Answer: Geologists measure earthquakes in two
ways.
1)
The
amount of earthquake damage or shaking that is felt is rated using the Modified
Mercalli Scale.
*The
Modified Mercalli Scale rates the amount of shaking from an earthquake. It is rated by people’s observations, without
the use of instruments. This scale is
used in regions where there aren’t many instruments to measure an
earthquake. It uses Roman numerals to
rate the damage and shaking at any given location.
2)
The
magnitude (SIZE) of an earthquake is measured on a seismograph using the
Richter Scale or the Moment Magnitude Scale.
*An
earthquakes magnitude (size) is a single number that geologists assign to an
earthquake based on the earthquake’s size.
*THE
EARLIEST MAGNITUDE SCALE IS CALLED THE RICHTER SCALE.
*The
Moment Magnitude Scale rates the total energy an earthquake releases.
A
magnitude of below 5 is a small earthquake and causes little damage.
A
magnitude above 6 is a large earthquake and can cause great damage.
The
most powerful earthquakes, with a magnitude of 8 or above, are rare and cause
tremendous damage.
How
is an epicenter located?
Answer: Geologists use seismic waves to locate an
earthquake’s epicenter using data from thousands of seismograph stations set up
all over the world.
How
do seismographs work?
Answer: Seismic waves cause a simple seismograph’s
drum to vibrate, which in turn causes the pen to record the drum’s
vibrations. The suspended weight with
the pen attached moves very little. This
allows the pen to stay in place and record the drum’s vibrations. The rest of the seismograph is anchored to
the ground and vibrates when seismic waves arrive.
What
is a seismogram?
Answer: The pattern of lines, called a seismogram, is
the record of an earthquake’s seismic waves produced by a seismograph.
What
patterns do seismographic data reveal?
Answer: Geologists have created maps, by using
seismographic data, of where earthquakes occur around the world to show that
earthquakes often occur along plate boundaries.
Where
in the United States are the possibilities of major earthquakes more likely?
Answer: Plates meet along the Pacific coast in
California, Washington state, and Alaska, causing many faults.
