EARTHQUAKES
MRS. BAKER
CJCB 2015
CAUSES OF EARTHQUAKES
• Earthquake – a shaking of Earth’s crust caused by a
release of energy.
• Occur for many reasons:
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Eruption of a volcano
Collapse of a cavern
Impact of a meteor
Strain that builds up along faults at or near boundaries
between lithospheric plates.  cause of most earthquakes
CAUSES OF EARTHQUAKES
• Elastic-rebound theory
• Friction prevents the plates from moving, so strain builds up,
causing the plates to deform.
• The strain will become great enough to overcome the
friction and the plates move, causing an earthquake.
• The plates then snap back to the shape that they had
before the earthquake, but are in different locations.
CAUSES OF EARTHQUAKES
• Fault – break in the lithosphere along which plate
movement has occurred.
• Hanging wall—rock on top of fault plane
• Footwall—rock below fault plane
• Focus – the point at which the first movement
occurs during an earthquake.
• Epicenter – the point on Earth’s surface directly
above the focus.
FOUR TYPES OF FAULTS
• Normal
• Reverse
• Thrust (lowangle reverse)
• Strike-slip
FOUR TYPES OF FAULTS
• Normal
• Hanging wall moves down relative to footwall
• Usually forms from stress at divergent boundary
FOUR TYPES OF FAULTS
• Reverse
• Hanging wall moves up relative to footwall
• Usually forms from compression at convergent boundary
• Thrust
• A low angle (<45 degrees) reverse fault
FOUR TYPES OF FAULTS
• Strike-slip
• Movement is horizontal
• Usually forms at a transform boundary
FAULTING, FOLDING, AND
MOUNTAINBUILDING
• When large blocks of crust are moved, they may be
tilted up to form mountains
• Blocks of crust can be pushed straight up to form
mountains
• One block may drop relative to another, creating
mountains and valleys
• Large scale compression and folding can result in
folded mountains and folded mountain ranges,
particularly when two continental plates meet at a
convergent boundary.
THREE TYPES OF SEISMIC WAVES
• P waves
• S waves
• Surface waves
BODY WAVES
• Body waves – waves that travel from the focus of an
earthquake through Earth.
• P waves
• Primary waves
• Compression or longitudinal waves (parallel to motion)
• Squeeze and stretch rock materials as they pass through
Earth.
• Can travel through any material – solid rock, magma,
ocean water, and air.
• Fastest of the wave types; first to be felt and recorded
BODY WAVES
• S waves
• shear waves or secondary waves
• Cause particles of rock material to move at right angles to
the direction in which the waves are traveling—transverse
waves
• Can travel through solid material, but not liquids or gases.
SURFACE WAVES
• Surface waves – earthquake waves that travel
along Earth’s surface.
• Travel both up-and-down and side-to-side
• Like ripples in a pond
• P and S waves produce surface waves
• Do much damage on Earth’s surface
SEISMOGRAPHS
• Seismograph – an instrument that detects and
records waves produced by earthquakes.
• Also called a seismometer
• Different types of seismographs record different
types of wave motion.
SEISMOGRAPHS
• A common type has a heavy weight attached to a
base anchored in bedrock.
• The weight stays almost perfectly still even when there is an
earthquake.
• Seismogram – a record sheet that records
earthquake movement.
INTERPRETING A SEISMOGRAM
• P waves travel faster than S waves and therefore
arrive at a seismograph station first.
• P and S waves produce different patterns on a
seismogram.
• As the waves travel farther from the epicenter, the S
waves will fall behind the P waves more and more.
• Can be used to know what cities are closer or
farther away from the epicenter.
LOCATING THE EPICENTER
• A seismogram tells the distance between the
epicenter and the recording station, but does not
give enough information to locate the epicenter.
• The distance is calculated using the difference between the
time the p wave is detected and the s wave is detected.
• Information from additional recording stations is
required.
• Three different seismograph stations are needed to pinpoint
the epicenter “TRIANGULATION”
LOCATING THE EPICENTER
• Knowing the distance a city is from the epicenter, a
circle can be drawn with a radius equal to that
distance.
• Draw circles for at least three cities and where they
intersect is the location of the epicenter.
MEASURING AN EARTHQUAKE’S
MAGNITUDE
• The magnitude of an earthquake indicates how
strong it is.
• The most commonly used scale is the Richter Scale.
• Each increasing number on the Richter Scale
indicates 32 times the energy of the number before.
MEASURING AN EARTHQUAKE’S
MAGNITUDE
• How much more powerful is a 4 magnitude
earthquake than a 3 magnitude?
• 32 times
• How much more powerful is an 8 magnitude
earthquake than a 5 magnitude?
• 32 x 32 x 32 = the difference in energy
MEASURING EARTHQUAKE ACTIVITY
• Mercalli Scale- measures relative intensity of
earthquakes by observing the effects on
Earth’s surface
• Scale goes from I (barely felt, if at all) to XII (total
destruction)
• Intensity is not a measure of energy (like
magnitude) but of effect on Earth’s surface
EARTHQUAKE ACTIVITY
AND PLATE TECTONICS
Earthquakes are concentrated at plate tectonic boundaries
• Deepest earthquakes along subduction zones
Plate Boundaries
Earthquake Activity
EARTHQUAKE ACTIVITY
AND PLATE TECTONICS
• The most earthquakes occur along the Ring of Fire,
the area around the edge of the Pacific Plate
• The Pacific Plate is the most active tectonic plate
EARTHQUAKES IN THE UNITED
STATES
• Every state within the United States has had some
type of seismic movement.
AREAS OF EARTHQUAKE ACTIVITY
• STRONG ACTIVITY:
California, Oregon,
and Washington
• Due to subduction
of the Juan de Fuca
Plate with the North
American Plate
AREAS OF EARTHQUAKE ACTIVITY
• Alaska
• due to subduction of
the Pacific Plate
• New Madrid Seismic Zone (MO)
• weakness and old faults due to
ancient (failed) rift zone
• earthquakes in response to movement
of North American Plate
HAWAII
• due to volcanic
activity
HOT SPOT MOVEMENT!
ARE THERE EARTHQUAKES IN VA?
• Yes!
• But Virginia is a stable area, NOT on the edge of a tectonic plate
• So earthquakes are irregular and very rarely over a 4.5 on the
Richter Scale
• However, stable ground means we feel it far away from epicenter
HAZARDS ASSOCIATED
WITH EARTHQUAKES
AND VOLCANOES
VOLCANIC HAZARDS
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Lava Flows
Ash Falls
Volcanic Bombs
Pyroclastic Flows
Lahars
Toxic Gases
Earthquakes
Tsunamis
More…
TEPHRA
- The material that is blown out of a volcano and into the air
during a violent eruption.
- This is also known as pyroclastic material. There a 5 general
categories of tephra that are primarily separated according to size:
Volcanic Dust
Volcanic Ash
Lapilli
Volcanic Blocks
Volcanic Bombs
PYROCLASTIC FLOWS
Pyroclastic flows are high density
mixtures of hot, dry rock fragments and
hot gases that move away from the
vent that erupted them at high speeds
(hundreds of miles per hour).
LAHARS
A volcanic mudflow.
- lethal mixtures of water and tephra
with consistency of wet concrete
- flow down the slopes of volcanoes
or down river valleys at rapid speeds,
similar to fast-moving streams of
water
- buries all in the way
- can carry huge boulders
TOXIC GASES
Sulfur dioxide (SO2
-
colorless gas with a pungent odor that irritates skin and the
tissues and mucous membranes of the eyes, nose, and throat
- creates haze that affects global temperatures
- contributes to acid rain
TOXIC GASES
CO2 (carbon dioxide):
- may become concentrated
at levels lethal to people
and animals.
- heavier than air.
Hydrogen Fluoride (HF)
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powerful caustic irritant
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can cause conjunctivitis, skin
irritation, bone degeneration and
mottling of teeth.
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significant cause of death and
injury in livestock during ash
eruptions and even afterwards, if
eat HF-tainted grass
1986: Lake Nyos, Cameroon
- Massive death within 15 miles
- CO2 gases due to extinct volcano
EARTHQUAKE HAZARDS
• Collapsing buildings claim the majority of lives,
but the destruction is often compounded by
• Tsunamis
• Mud Slides
• Fires
• Floods
EARTHQUAKE DAMAGE
Haiti Earthquake7.0 Magnitude
January 12, 2010
-230,000 people died
-300,000 people injured
-1,000,000 people homeless
EARTHQUAKE DAMAGE
Loma Prieta Earthquake“World Series Earthquake”
6.9 Magnitude
October 17, 1989
- Heaviest damage in San
Francisco Bay area, 60
miles north of epicenter
-63 deaths, 3,757 injuries
- estimated $6 billion in
property damage
LOMA PRIETA EARTHQUAKE DAMAGE
at Stanford University
Room where
Mrs. Brause
was when it hit
EARTHQUAKE SIDE EFFECTS
• Tsunami – a giant sea wave
typically produced by an
underwater earthquake.
• Also can be caused by
underwater landslides and
volcanoes
• Known as a tidal wave.
• A tsunami can travel long
distances at speeds up to
500 mph
• In 1946, an 7.8 magnitude
earthquake near Alaska
caused a 46-foot Tsunami
that reached Hawaii
• 80% of tsunamis in Ring of Fire
BOXING DAY TSUNAMI
DECEMBER 26, 2004
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Earthquake with epicenter off west coast of Sumatra,
- magnitude 9.1–9.3 -- the third largest earthquake ever recorded
on a seismograph.
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longest duration of faulting ever observed, between 8.3 and 10
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located in a subduction zone
minutes.
Tsunami:
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Earthquake triggered a series of devastating tsunamis along the
coasts of most landmasses bordering the Indian Ocean; Indonesia
was the hardest-hit country, followed by Sri Lanka, India, Thailand.
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coastal communities inundated with waves up to 98 ft high.
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over 230,000 people killed in fourteen countries; ne of the deadliest
natural disasters in recorded history.
JAPAN EARTHQUAKE &
TSUNAMI
Japan Earthquake 2011:
8.9 Magnitude Earthquake Hits,
30-Foot Tsunami Triggered
The earthquake:
- shifted Earth on its axis of
rotation
- -shortened the length of a day
by about a microsecond
- moved Japan's main island of
Honshu eastward by 2.4 m
- most deaths due to Tsunami
PREVENTING EARTHQUAKE DAMAGE
• Scientists study buildings after earthquakes to see
which types of structures sustain the most and least
amount of damage.
• Building codes in earthquake zones are designed to
prevent structural collapse.
• Leads to better designs for bridges, buildings, etc.
EARTHQUAKE RISK
• In the United States, many places are obvious
because they lie along plate boundaries.
• Alaska
• California
• Western states
• New Madrid Fault – Missouri, not so obvious, not
along plate boundaries – but some of the largest
earthquakes in U.S. history.
PREDICTING EARTHQUAKES
• Must be able to predict three things:
• Where the earthquake will occur.
• When the earthquake will occur.
• The magnitude of the earthquake that will occur.
• Can make long-term predictions based on past
earthquake activity.
• Scientists can also identify seismic gaps which are
areas where faults have not moved over a period. 
May indicate that tension is building and an
earthquake might be developing.