Chapter 8
Earthquakes and
Earth’s Interior
Section 8.1
What is an
Earthquake?
What is an earthquake?
• An earthquake is the vibration of Earth produced by the
rapid release of energy.
– Example: 1906 San Francisco Earthquake.
• Earthquakes usually occur when rocks under stress
suddenly shift along a fault.
– Stress: A force that can change the size and shape of rocks.
– Fault: Fractures in the Earth where movement occurred.
• The area along a fault where slippage first occurs is called
the focus of an earthquake.
• The point on the earth’s surface directly above the focus is
called the epicenter.
• When an earthquake occurs, seismic waves radiate outward
in all directions from the focus.
What is an earthquake?
A fault is
A. A place on Earth where earthquakes
cannot occur.
B. A fracture in the Earth where movement
has occurred.
C. The place on Earth’s surface where
structures move during an earthquake.
D. Another name for an earthquake.
An earthquake’s epicenter is
A. The place on the surface directly above
the focus.
B. A spot halfway between the focus and the
surface.
C. The spot below the focus.
D. Any spot along the nearest fault.
When an earthquake occurs, energy radiates in all
directions from its source, which is called the
A.
B.
C.
D.
Epicenter.
Focus.
Fault.
Seismic Center.
Earthquakes are usually associated with
A.
B.
C.
D.
Violent weather.
Faults.
Large cities.
The east coast of North America.
What is an earthquake?
• Geologists explain many earthquakes by the
elastic rebound hypothesis.
• This hypothesis states that when the stress in
rocks becomes to great, they fracture,
separate, and spring back to their original
shape, or rebound.
• As they fracture and slip into new positions,
rocks along a fault release energy in the form
of vibrations called seismic waves.
What is an earthquake?
Which of the following causes earthquakes?
A.
B.
C.
D.
Elastic Rebound.
Richter Scale.
Release of Heat.
Frictional Heating.
The hypothesis that explains the release of energy
during an earthquake is called the
A.
B.
C.
D.
Richter Hypothesis.
Moment Magnitude Hypothesis.
Vibration Hypothesis.
Elastic Rebound Hypothesis.
Most earthquakes are produced by the rapid
release of which kind of energy stored in rock
subjected to great forces?
A.
B.
C.
D.
Chemical
Thermal
Elastic
Mechanical
During an earthquake, the ground surface
A.
B.
C.
D.
Moves only in a horizontal direction.
Moves only in a vertical direction.
Can move in any direction.
Does not move.
What is an earthquake?
• This release of energy often increases the
stress in other rocks along the fault, causing
them to fracture and spring back.
• This reaction is the reason that major
earthquakes are usually followed by a series
of smaller tremors called aftershocks.
• These aftershocks are usually much weaker
than the main earthquake, but they can
sometimes destroy structures weakened by
the main quake.
What is an earthquake?
• Small earthquakes called foreshocks often come before a
major earthquake.
– These can happen days or even years before the major quake.
• The San Andreas Fault is the most studied fault system in
the world.
– Studies have shown that displacement has occurred along segments
that are 100 to 200-kilometers long (63 to 125-miles).
• Some segments move slowly, which is known as fault creep.
• Other segments regularly slip and produce small
earthquakes.
• Some segments stay locked and store elastic energy for
hundreds of years before they break and cause great
earthquakes.
The adjustments of materials that follow a major
earthquake often generate smaller earthquakes
called
A.
B.
C.
D.
Foreshocks.
Surface waves.
Aftershocks.
Body waves.
Major earthquakes are sometimes preceded by
smaller earthquakes called
A.
B.
C.
D.
Aftershocks.
Focus shocks.
Surface waves.
Foreshocks.
The slow continuous movement that occurs along
some fault zones is referred to as
A.
B.
C.
D.
Slip.
Creep.
Fracture.
A foreshock.
Small foreshocks that precede a major earthquake
occur
A. From the day of the major earthquake to
days after the earthquake.
B. Only on the day of the major earthquake.
C. Days or years before the major
earthquake.
D. Only on the day before the major
earthquake.