Lessons 1-4

1
Earthquakes

• Lessons 1-4

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• Lesson 1
• What are earthquakes and where do they occur

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Where do Earthquakes Occur?

• Earthquakes can occur near the Earths surface or
  far below the surface.
• Most earthquakes occur at plate boundaries, but
  some happen at faults located in the middle of
  tectonic plates.
• http//www.dosecc.org/html/volcanic_monitoring.htm
  l

How many earthquakes have already occurred
today?
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PLATE BOUNDARIES
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Earthquake Locations Around the World
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What Causes Earthquakes?

• Earthquakes are caused by movement along faults.
• When stress is placed on rocks it deforms, or
  changes.
• This is called Elastic Deformation (remember
  faults and folds, tension and compression)
• Rock is stretched and bent until it can no longer
  take the stress.
• When enough stress builds up in the rock it, it
  slips and energy is released.
• The rock then returns to its original shape. This
  is called Elastic Rebound. Think of a rubber
  band, you can only stretch it so far until it
  breaks and return to its original shape.
• This energy is felt as an earthquake.

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Elastic
ELASTIC REBOUND
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Earthquakes in Alabama??

• Do we live near a plate boundary?
• Do we live near a fault?

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The New Madrid Fault

• If there is no plate boundary in the middle of
  the United States, why did these earthquakes take
  place?
• Geologists are beginning to understand the
  answer. The New Madrid Fault Zone is part of an
  ancient plate boundary. In this area, the North
  American Plate tried to form a divergent plate
  boundary about 500 million years ago. The
  splitting stopped before new plates could form.
  The faults in the New Madrid Zone are remnants of
  this old event. Earthquakes occur because the
  North American Plate is still "settling down".
  The faults in the New Madrid Zone do not reach
  the Earths surface. They are buried beneath
  thousands of feet of rock and sediment deposited
  by the Mississippi River. Geologists have located
  them by looking at the patterns of earthquakes in
  the zone.

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Several of the largest earthquakes ever recorded
in the United States occurred in the Midwest, far
from any plate boundary. These earthquakes took
place in an area called the New Madrid Fault
Zone, named after the town of New Madrid,
Missouri.
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New Madrid Fault

• Over a three-month period in the winter of 1811
  to 1812, the New Madrid Fault Zone was struck by
  three huge earthquakes estimated to be greater
  than magnitude 8.0
• The New Madrid Fault is what causes Alabama to
  experience earthquakes.

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• The map shows the earthquakes recorded in
  Alabama since 1886.

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The last earthquake to occur in Alabama was on
July 27, of this year. It measured a 2.6 on the
Richter scale. This was not a very strong
earthquake, but it was recorded by a seismograph,
an instrument used to measure earthquakes.
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Lesson 2
Faults and Earthquakes
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3 Types of Faults associated with Earthquakes
PLATE MOTION FAULT TYPE
Transform Strike Slip Fault
Convergent Reverse Fault
Divergent Normal Fault
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Strike-Slip Fault occurs at a Transform Boundary
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Reverse Fault occurs at a Convergent Boundary
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Normal Faults occur at Divergent Boundaries
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Chapter 8 Sections 1 Earthquakes and Faults
Organizer
PLATE MOTION FAULT TYPE
Transform Strike Slip Fault
Convergent Reverse Fault
Divergent Normal Fault
Plates move past each other
Fault blocks move past each other
Plates move together
Fault blocks move together
Plates move apart
Fault blocks move apart
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Lesson 3
SEISMIC WAVES
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How do Earthquake Waves Travel?

• Energy released from moving plates and faults
  travels through the Earth as waves.
• These waves are called seismic waves.

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Types of Seismic Waves

• 1. BODY WAVES Seismic waves that travel through
  the Earth.
• 2. SURFACE WAVES Seismic waves that travel along
  the surface.
• WAVES TRAVEL
• 1.At different speeds and
• 2 In different ways
• Depending on what kind of material they are
  moving through.

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Body Waves

• There are two types of body waves
• P-waves
• S-waves

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P-waves

• P-waves are pressure waves.
• P-waves travel through solid, liquids and gases.
• P-waves are the fastest waves.
• P-waves are the first waves to be detected and
  the first waves to arrive.
• P-waves are also called primary waves because
  they arrive first.
• P-waves cause rock to squeeze and stretch.
  Imagine a slinky!
• The area of the Earth that does not receive
  seismic energy is called the shadow zone.

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1.P-Waves
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2. S-waves

• S-waves are the second fastest waves.
• S-waves are also called secondary waves because
  they arrive second.
• S-waves are slower than P-waves.
• S-waves move rock from side to side.
• S-waves cant travel through parts of the Earth
  that are completely liquid.

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S-Waves
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3. Surface Waves

• Surface waves move along the surface of the
  Earth.
• Surface waves can move up, down and around or
  side to side.
• Surface waves move the slowest and cause the most
  destruction.

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Surface Waves
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Seismic Wave Arrival

• First- P-waves
• Second- S-waves
• Third- Surface Waves

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Shadow Zone
The shadow zone results from S waves being
stopped entirely by the liquid core and P waves
being bent (refracted) by the liquid core.
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Moho Zone

• The Moho is the boundary between the crust and
  the mantle in the earth. This is a depth where
  seismic waves change velocity, or speed. They
  tend to increase at the location.

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Quiz

• 1. Most Earthquakes occur along ________________.
• 2. The first seismic waves to arrive
  are______________.
• 3. The second seismic waves to arrive are
  _____________.
• 4. The last seismic waves to arrive
  are_______________.
• 5. Which seismic waves travel the
  fastest?___________
• 6. Which type of seismic wave can move through a
  solid, liquid or a gas?________________
• 7. Which seismic wave cannot travel through
  material that is completely liquid?______________
• 8. Which seismic waves are the slowest and the
  most destructive?_______________

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Earthquake Measurement
Lesson 4
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Seismograph

• A seismograph is an instrument used by scientists
  to measure earthquakes.
• Seismologists who study earthquakes can determine
  when an earthquake started by noting the arrival
  times of P-waves and S-waves.
• A seismograph records vibrations in the Earth and
  determines the strength and location of an
  earthquake.

Ancient Chinese Seismograph. The ball would drop
from the dragon to the frog. It told the people
which direction the earthquake come from.
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Seismograms
0 1 2 3 4
5 6 7 8
Time in Minutes
1. How many minutes did it take for the P-Waves
to arrive? 2. How many minutes did it take for
the S-waves to arrive? 3. How long did the
surface waves last?
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Epicenter

• The epicenter is the point on the Earths surface
  directly above an earthquakes starting point.

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Focus

• The focus is the point inside the Earth where the
  earthquake begins.
• The epicenter is located directly above the focus.

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Measuring Earthquakes

• There are two major ways earthquakes are
  measured
• Richter Scale
• 2. Mercalli Scale

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Richter Scale/Measures Magnitude

• The Richter Scale measures magnitude.
• The measurements are given in numbers.
• Measures the energy released by an earthquake
• Earthquake Severity-Energy released by an
  earthquake.
• Richter Earthquake Magnitudes Effects
• Less than 3.5 Generally not felt, but recorded.
• 3.5-5.4 Often felt, but rarely causes damage.
• Under 6.0 At most slight damage to well-designed
  buildings. Can cause major damage to poorly
  constructed buildings over small regions.
• 6.1-6.9 Can be destructive in areas up to about
  100 kilometers across where people live.
• 7.0-7.9 Major earthquake. Can cause serious
  damage over larger areas.
• 8 or greater Great earthquake. Can cause serious
  damage in areas several hundred kilometers
  across.

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Mercalli Scale/Measures Intensity

• In seismology a scale of seismic intensity is a
  way of measuring or rating the effects of an
  earthquake at different sites.
• The Modified Mercalli Intensity Scale is
  commonly used in the United States by
  seismologists seeking information on the severity
  of earthquake effects. Intensity ratings are
  expressed as Roman numerals between I at the low
  end and XII at the high end.

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• I. People do not feel any Earth movement.
• II. A few people might notice movement if they
  are at rest and/or on the upper floors of tall
  buildings.
• III. Many people indoors feel movement. Hanging
  objects swing back and forth. People outdoors
  might not realize that an earthquake is
  occurring.
• IV. Most people indoors feel movement. Hanging
  objects swing. Dishes, windows, and doors rattle.
  A few people outdoors may feel movement. Parked
  cars rock.
• V. Almost everyone feels movement. Doors swing
  open or close. Dishes are broken. Pictures on the
  wall move. Small objects move or are turned over.
  
• VI. Everyone feels movement. People have trouble
  walking. Objects fall from shelves. Pictures fall
  off walls. Furniture moves. Plaster in walls
  might crack. Trees and bushes shake.

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VII. People have difficulty standing. Drivers
feel their cars shaking. Some furniture breaks.
Loose bricks fall from buildings. Damage is
slight to moderate in well-built buildings
considerable in poorly built buildings. VIII.
Drivers have trouble steering. Houses that are
not bolted down might shift on their foundations.
Tall structures such as towers and chimneys might
twist and fall. Well-built buildings suffer
slight damage. Poorly built structures suffer
severe damage. Tree branches break. Hillsides
might crack if the ground is wet. IX. Well-built
buildings suffer considerable damage. Houses that
are not bolted down move off their foundations.
Some underground pipes are broken. The ground
cracks. X. Most buildings and their foundations
are destroyed. Some bridges are destroyed. Dams
are seriously damaged. Large landslides occur.
Water is thrown on the banks of canals, rivers,
lakes. The ground cracks in large areas. Railroad
tracks are bent slightly. XI. Most buildings
collapse. Some bridges are destroyed. Large
cracks appear in the ground.. Railroad tracks are
badly bent. XII. Almost everything is destroyed.
Objects are thrown into the air. The ground moves
in waves or ripples. Large amounts of rock may
move. As you can see from the list above, rating
the Intensity of an earthquake's effects does not
require any instrumental measurements. Thus
seismologists can use newspaper accounts,
diaries, and other historical records to make
intensity ratings of past earthquakes.
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• What was the magnitude of the Hawaii earthquake?
• 2. Where was the intensity the greatest?
• 3.According to the Mercalli Scale on what island
  did the most damage likely occur?

Oahu
IV
Maui V-VI
Hawaii
6.7
VII
VI
V
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Mercalli Intensity Scale

1. What is the intensity at Monterey?
2. What is the intensity at the epicenter?
3. What is the intensity at San Jose?
4. What is the intensity at Santa Cruz?
5. What is the intensity at Smith?

Smith
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Earthquakes in Alabama?
Largest Earthquake in Alabama 1916 South of
Birmingham, in Irondale 5.1 on the Richter
Scale VII (7) on Mercalli Scale