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Chapter Menu
Lesson 1: Earthquakes and
Plate Boundaries
Lesson 2: Earthquakes and
Seismic Waves
Lesson 3: Measuring Earthquakes
Lesson 4: Earthquake Hazards
and Safety
Click on a hyperlink to view the corresponding lesson.
6.1 Earthquakes and Plate Boundaries
earthquake
elastic strain
focus
• Fault: fracture along which rock
on one side has moved relative
to rock on the other side
• Interact: to act on each other
6.1 Earthquakes and Plate Boundaries
Earthquake
• The rupture and sudden movement of
rocks along a fault.
• A fault is a fracture surface along which
rocks can slip.
• Majority of earthquakes occur in
Earth’s crust.
• Part of the energy released from
earthquakes spreads as complex waves.
6.1 Earthquakes and Plate Boundaries
Earthquake (cont.)
• Heat energy moves through Earth’s mantle
by convection
• Some of the heat energy is transformed
into kinetic energy
• Kinetic energy is stored as elastic strain
• When rocks cannot change shape
anymore, faults break.
6.1 Earthquakes and Plate Boundaries
Elastic Strain Energy
• Elastic strain is the energy stored as a
material changes in shape.
• When rocks can no longer change shape—
the fault breaks and slips, causing
earthquakes.
6.1 Earthquakes and Plate Boundaries
Elastic Strain Energy (cont.)
Elastic Strain
When elastic strain builds
up, rocks rupture where
they are weakest. Either a
new fault will form, or the
rupture will occur along an
older fault.
6.1 Earthquakes and Plate Boundaries
Focus
• The focus is the location on the fault
where an earthquake begins.
• The closer the focus is to the surface, the
stronger the shaking will be.
6.1 Earthquakes and Plate Boundaries
Fault Zones
• Plate boundaries are usually made of multiple
faults called zones that are 40–200 km wide.
6.1 Earthquakes and Plate Boundaries
Plate Boundaries and Earthquakes
• Lithospheric plates interact at different plate
boundaries and produce earthquakes.
• Earthquake size and depth and fault type
depend on the type of plate boundary.
6.1 Earthquakes and Plate Boundaries
Plate Boundaries and Earthquakes (cont.)
6.1 Earthquakes and Plate Boundaries
Divergent Plate Boundaries
• Rocks break under tension stress, forming
normal faults
• Most earthquakes at divergent plate
boundaries occur at relatively shallow
depths in the crust and are relatively small
in size.
6.1 Earthquakes and Plate Boundaries
Convergent Plate Boundaries
• Rocks break under compression stress,
forming reverse faults.
• Deepest earthquakes happen at
subduction zones
• Result in most devastating earthquakes in
Earth’s history.
6.1 Earthquakes and Plate Boundaries
Transform Plate Boundaries
• Plates slide horizontally past one another with
shear stress, forming strike-slip faults.
• Earthquakes mainly occur at relatively
shallow depths.
• When boundaries run through continents,
they can cause major earthquakes.
6.1 Earthquakes and Plate Boundaries
Earthquakes Away from
Plate Boundaries
6.1 Earthquakes and Plate Boundaries
Earthquakes Away from
Plate Boundaries (cont.)
• New Madrid Earthquakes of 1911
• Millions of years ago, a long zone of
intense faulting was formed when the crust
began to pull apart, but did not break
completely.
• Today, the crust is being compressed, or
squeezed together.
Earthquakes Away from Plate Boundaries
• May occur at old, buried faults
• Continents may have started to split,
but then stopped
• Stresses at today’s plate boundaries
build up inside the plate
• Occur rarely
Causes of Earthquakes
• Earthquakes occur when elastic strain
builds up to the point that rocks break and
move
• Energy is released as earthquakes and
waves
• Plates boundaries can rupture and move
as earthquakes
• Some earthquakes occur in the middle of
plates, far from boundaries
Questions pg. 57
When does a fault rupture?
What causes seismic waves?
Questions pg. 58
• Do the same type of earthquakes occur at
all plate boundaries?
• Can earthquakes occur away from plate
boundaries? Why?
6.1 Earthquakes and Plate Boundaries
Strike-slip faults occur at what type
of plate boundary?
A convergent plate
boundary
B transform plate
boundary
C divergent plate
boundary
0%
0%
D
0%
C
D subduction plate
boundary
0%
B
A
B
C
D
A
1.
2.
3.
4.
6.1 Earthquakes and Plate Boundaries
The focus of an earthquake is ____.
A where an earthquake
is first felt on the
surface of Earth
B where an earthquake
dissipates
C where the fault and a
plate meet
0%
0%
D
0%
C
D where an earthquake
begins
0%
B
A
B
C
D
A
1.
2.
3.
4.
6.1 Earthquakes and Plate Boundaries
D
C
Which boundary is associated with
earthquakes that occur at relatively
shallow depths and are small in size?
A divergent plate
boundary
B convergent plate
boundary
C transform plate
boundary
0%
0%
0%
0%
D subduction plate
boundary
B
A
B
C
D
A
1.
2.
3.
4.
6.2 Earthquakes and Seismic Waves
seismic wave
epicenter
primary wave
secondary wave
• Wave: a wave transfers energy from place
to place
• Internal: existing within the limits or
surface of something
6.2 Earthquakes and Seismic Waves
Seismic Wave
• Waves of energy that are produced at the
focus of an earthquake.
• Waves move outward from the focus in all
directions.
6.2 Earthquakes and Seismic Waves
Epicenter
• The point on
Earth’s surface
directly above the
earthquake’s
focus.
How do seismograph
stations help determine
an earthquake’s
epicenter?
6.2 Earthquakes and Seismic Waves
Primary Waves (P-waves)
6.2 Earthquakes and Seismic Waves
Secondary Waves (S-waves)
6.2 Earthquakes and Seismic Waves
Surface Waves
Surface Waves (cont.)
6.2 Earthquakes and Seismic Waves
Using Seismic Wave Data
• Used to determine the composition of
Earth’s interior
• If close to the focus, the S-wave is not very
far behind the P-wave.
• If far from the focus, the S-wave travels far
behind the P-wave.
• P-waves arrive first, then S-waves, and
surface waves last
6.2 Earthquakes and Seismic Waves
Mapping Earth’s Internal Structure
• Earth’s internal structure can be determined
by analyzing the paths of seismic waves.
• Waves bounce or bend as they approach a
new layer
• Rock densities make waves curve as they
pass through Earth
6.2 Earthquakes and Seismic Waves
Mapping Earth’s Internal Structure (cont.)
• Shadow zones are areas that do not
receive seismic waves.
– Secondary waves only travel through
solids and cannot penetrate the outer core.
– Primary waves can travel through solids
and their paths bend through liquids.
– Because primary waves bend, scientists
believe that the outer core is composed
of liquid.
Shadow Zone
• An area that receives NO seismic waves
• S-waves pass only through solids, so outer
core must be liquid
Mapping Earth’s Internal Structure (cont.)
Questions pg. 60
What happens to the energy
released from the focus as it
moves some distance away?
What are the three types of seismic
waves?
Questions pg. 61
What happens to primary and
secondary waves in solids and
liquids?
How did scientists make inferences
about Earth’s inner structure?
6.2 Earthquakes and Seismic Waves
Surface waves cause rock particles
to move with a(n) _____.
A side-to-side motion
B rolling motion
C up-and-down and
side-to-side motion
0%
0%
0%
D
0%
C
D side-to-side and
rolling motion
B
A
B
C
D
A
1.
2.
3.
4.
6.2 Earthquakes and Seismic Waves
What is a characteristic of P-waves?
A They cause rock particles
to vibrate perpendicular to
the direction that waves
travel.
B They cause rock particles
to vibrate in the same
direction that waves travel.
C They only travel through
solids.
0%
0%
D
D They are the slowest
seismic wave.
0%
C
0%
B
A
B
C
D
A
1.
2.
3.
4.
6.2 Earthquakes and Seismic Waves
Which type of wave causes the most
destruction at Earth’s surface?
A P-wave
B S-wave
C surface wave
0%
0%
0%
D
0%
C
D combination of
P-wave and surface
wave
B
A
B
C
D
A
1.
2.
3.
4.
6.3 Measuring Earthquakes
seismograph
seismogram
sediment: rock material that is broken
down into smaller pieces or dissolved
in water
Indicate: to show something
6.3 Measuring Earthquakes
Measuring Earthquakes
• Scientists determine size of earthquakes by
measuring how much the rock slips along
the fault.
• They also analyze the heights of the
seismic waves, which indicate how much
energy is released by an earthquake.
6.3 Measuring Earthquakes
Seismograph
• Records size,
direction, and
the movement
time of ground
• Records the
arrival times of
the P- and Swaves
6.3 Measuring Earthquakes
Seismogram
• Record of the seismic waves
• Used to calculate the size and locations
of earthquakes
6.3 Measuring Earthquakes
Reading a Seismogram
• Wave heights indicate the amount of
ground motion for each type of wave.
• Difference between
the arrival times of
P-waves and Swaves determines
the distance of the
seismograph from
the epicenter.
6.3 Measuring Earthquakes
Locating an Epicenter
• Triangulation is used to locate the epicenter.
• This method is based on the speeds of the
seismic waves.
• At least three seismographs must record
the distances.
6.3 Measuring Earthquakes
1. Find the arrival time differences.
6.3 Measuring Earthquakes
2. Find the difference from the
epicenter.
6.3 Measuring Earthquakes
3. Plot the distance on a map.
• Plot the P-wave and S-wave arrival time
differences against time. Use the graph to
find the distance to the epicenter
• Plot the distance on a map. Draw a circle
with a radius equal to that distance.
• Plot distances from at least 3
seismographs. The place where the
circles intersect is the epicenter.
6.3 Measuring Earthquakes
Measuring Earthquake Size
• Magnitude measures the amount of energy
released by an earthquake.
• Determined by the buildup of elastic strain
energy in the crust, at place where rupture
occurs
• Magnitude scale is based on record of
height of ground motion and ranges
from 0–9.
• Richter Magnitude Scale
6.3 Measuring Earthquakes
Moment Magnitude Scale
• Used today because it is a more accurate
scale for measuring earthquake size.
• Based on the amount of energy released
during an earthquake.
Modified Mercalli Scale
• Measures the amount of geologic and
structural damage an earthquake causes
• This describes the “intensity” of an
earthquake
• Uses Roman Numeral values from I to X+
6.3 Measuring Earthquakes
Earthquake Intensity
• Intensity values vary and depend on the
distance from the epicenter and the local
geology.
• Loose sediments or fill shake more
violently than rocks do.
• Usually, the maximum intensity is found near
the epicenter.
• The magnitude of an earthquake DOES NOT
CHANGE. The intensity (how much the
ground shakes) CAN CHANGE.
Questions pg. 63
How do scientists measure an
earthquake?
Can a scientist find the focus of an
earthquake with only one
seismograph? Why?
6.3 Measuring Earthquakes
D
C
What information should be known in order to
determine the epicenter?
A arrival time of P-waves and
surface waves at two
seismograph stations
B arrival time of P- and
S-waves at two
seismograph stations
C arrival time of P- and
S-waves at three
seismograph stations
0%
0%
0%
0%
D arrival time of P-waves and
surface waves at three
seismograph stations
B
A
B
C
D
A
1.
2.
3.
4.
6.3 Measuring Earthquakes
Triangulation is used to determine an
earthquake’s ____.
A P-waves
B S-waves
C epicenter
D magnitude
0%
0%
D
0%
C
0%
B
A
B
C
D
A
1.
2.
3.
4.
6.3 Measuring Earthquakes
What two factors influence intensity
values?
A population and distance
from the epicenter
B distance from the
epicenter and distance
from the ocean
C population and
local geology
0%
0%
0%
D
0%
C
D local geology and
distance from
the epicenter
B
A
B
C
D
A
1.
2.
3.
4.
6.4 Earthquake Hazards
and Safety
Liquefaction: process in which
earthquake shaking makes loose
sediment behave like liquid
Tsunami: ocean wave caused by
earthquakes
Vocabulary
• San Andreas Fault: fault zone that forms a
transform plate boundary between the
Pacific and North American Plates
• Securely: free from risk of loss
6.4 Earthquake Hazards and Safety
Avoiding Earthquake Hazards
6.4 Earthquake Hazards and Safety
Earthquake Hazards
• Most injuries result from the collapse of
buildings and other structures.
• Other hazards that might result from an
earthquake include fires, landslides, loose
sediment, and tsunamis.
• Earthquakes can cause:
• Collapse of structures
• Fire
• Landslides
• Loose sediments
• Tsunamis
6.4 Earthquake Hazards and Safety
Liquefaction
• The process by which shaking makes
loose sediment move like a liquid.
• When liquefaction occurs in soil under
buildings, buildings sink into the soil and
collapse
An
earthquake
occurs
under the
ocean
The seafloor
moves
suddenly
The movement pushes against the water,
causing powerful waves.
6.4 Earthquake Hazards and Safety
Tsunami
• Powerful ocean waves caused by
sudden movement of seafloor.
• Water along shoreline might move back
rapidly toward the sea before the wave
crashes on shore.
How do scientists recognize hazards?
• Scientists use geologic maps to
identify areas with loose
sediment and other places where
landslides, liquefaction, or
tsunamis are likely to occur.
Building safety
• Types of Buildings:
– Buildings made of flexible materials
generally suffer less damage than
buildings made of brittle materials
– Single-story buildings are less
susceptible to damage than taller
buildings
Building safety continued
• Earthquake resistant structures
– Some new buildings are supported by
flexible, circular moorings
– In other buildings, steel rods are used to
reinforce building walls
Safety indoors
• Move away from windows and objects that
can fall
• Take shelter in an interior doorway or
under a sturdy table or desk
• Have adults shut off water and gas if
damaged
Outdoor safety
• Stay in the open, away from power lines
• Stay away from damaged buildings
• Stay away from beaches.
Questions pg. 66
What kind of hazards result from
earthquakes?
Questions pg. 67
How can buildings be made more
earthquake-proof?
What should YOU do in an
earthquake?
6.4 Earthquake Hazards and Safety
What occurs when ground shaking
causes loose sediment to act like a
liquid?
A convection
B deposition
C subduction
D liquefaction
0%
0%
D
0%
C
0%
B
A
B
C
D
A
1.
2.
3.
4.
6.4 Earthquake Hazards and Safety
What causes a tsunami?
A liquefaction
B sudden movement of
the seafloor
C sudden movement of
the continents
D magnitude
0%
0%
D
0%
C
0%
B
A
B
C
D
A
1.
2.
3.
4.
6.4 Earthquake Hazards and Safety
What is a warning sign of a tsunami?
A beach erosion
B flash flooding
C water moving back
rapidly toward
the sea
0%
0%
0%
D
0%
C
D ships washing up
on shore
B
A
B
C
D
A
1.
2.
3.
4.
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Concepts in Motion
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Virtual Lab
Click on a hyperlink to view the corresponding feature.
What characteristics of an earthquake
are associated with a convergent plate
boundary?
A compression, very
deep earthquakes
B strike-slip, very
shallow earthquakes
C tension, very
shallow earthquakes
0%
0%
0%
D
0%
C
D tension, very
deep earthquakes
B
A
B
C
D
A
1.
2.
3.
4.
S-waves ____.
A only travel
through liquids
B are the first waves to
reach the seismograph
C only travel
through solids
0%
0%
0%
D
0%
C
D generally cause the
most damage at
Earth’s surface
B
A
B
C
D
A
1.
2.
3.
4.
What is magnitude?
A measure of the
distance between the
focus and the epicenter
B measure of the
distance between the
P- and S-waves
C measure of triangulation
0%
0%
0%
D
0%
C
D measure of the amount
of energy released by
an earthquake
B
A
B
C
D
A
1.
2.
3.
4.
Most injuries from an earthquake
result from ____.
A the shaking of Earth
B the collapse
of structures
C sink holes
D flash floods
0%
0%
D
0%
C
0%
B
A
B
C
D
A
1.
2.
3.
4.
What is a shadow zone?
A area that does not
receive seismic waves
B area directly above
the focus
C area directly above
the epicenter
0%
0%
0%
D
0%
C
D a fault
B
A
B
C
D
A
1.
2.
3.
4.
SCI 1.g
Where is the maximum intensity of an
earthquake felt?
A focus
B epicenter
C fault
D inland
0%
0%
D
0%
C
0%
B
A
B
C
D
A
1.
2.
3.
4.
SCI 1.e
What is the term for the energy
stored as a material changes in
shape?
A elastic strain
B kinetic energy
C plastic strain
D potential energy
0%
0%
D
0%
C
0%
B
A
B
C
D
A
1.
2.
3.
4.
SCI 7.g
If you are far from the focus of an
earthquake, ____.
A the S-wave travels far
behind the P-wave
B the P-wave travels far
behind the S-wave
C the S- and P-wave have
the same arrival time
0%
0%
0%
D
0%
C
D the S-wave and surface
wave have the same
arrival time
B
A
B
C
D
A
1.
2.
3.
4.
SCI 1.g
What method is used to determine
the epicenter of an earthquake?
A triangulation
B visual observation
C identifying where
the most damage
is located
0%
0%
0%
D
0%
C
D by measuring the size
of the earthquake
B
A
B
C
D
A
1.
2.
3.
4.
SCI 1.g
Which area would be the best for an
apartment complex?
A area with solid bedrock
B a bed of loose sediment
C an area built of landfill
D where the soil is sandy
0%
0%
D
0%
C
0%
B
A
B
C
D
A
1.
2.
3.
4.
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