Earthquakes by pengxiang


									Lessons 1-4
     Lesson 1:
What are earthquakes
 and where do they
   Where do Earthquakes Occur?
 Earthquakes can occur near the Earth’s
  surface or far below the surface.
 Most earthquakes occur at plate boundaries,
  but some happen at faults located in the
  middle of tectonic plates.
Earthquake Locations Around the World
What Causes Earthquakes?
• Earthquakes are caused by movement along
• When stress is placed on rocks it deforms, or
• 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.

     Earthquakes in Alabama??
   Do we live near a plate boundary?

   Do we live near a fault?
          The New Madrid Fault
   If there is no plate boundary in the middle of the
    United States, why did these earthquakes take
   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
    Earth’s 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.
     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,
   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.
   The map shows
    the earthquakes
    recorded in
    Alabama since
The last
earthquake to
occur in Alabama
was on July 27,
of this year. It
measured a 2.6
on the Richter

This was not a
very strong
earthquake, but it
was recorded by
a seismograph,
an instrument
used to measure
Lesson 2
 3 Types of Faults associated
      with Earthquakes

Transform      Strike –Slip Fault

Convergent     Reverse Fault

Divergent      Normal Fault
Strike-Slip Fault occurs at a
    Transform Boundary
Reverse Fault occurs at a
 Convergent Boundary
Normal Faults occur at Divergent
     Chapter 8: Sections 1: Earthquakes and Faults:
PLATE MOTION                    FAULT TYPE
Transform   Plates move past    Strike –Slip Fault
            each other          Fault blocks move past each other

Convergent Plates move together Reverse Fault
                                Fault blocks move together

Divergent   Plates move apart   Normal Fault
                                Fault blocks move apart
Lesson 3
How do Earthquake Waves Travel?
   Energy released from moving
    plates and faults travels through
    the Earth as waves.
   These waves are called seismic
       Types of Seismic Waves
1. BODY WAVES: Seismic waves that travel
  through the Earth.
2. SURFACE WAVES: Seismic waves that travel
  along the surface.

    1.At different speeds and
    2 In different ways
    Depending on what kind of material
        they are moving through.
        Body Waves
• There are two types of body waves:
• P-waves
• S-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
   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.
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 can’t travel through parts of the
    Earth that are completely liquid.
         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.
Surface Waves
Seismic Wave Arrival
 • First- P-waves

 • Second- S-waves

 • Third- Surface Waves
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.
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
• 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
 Lesson 4
 A seismograph is an instrument used by scientists to measure
 Seismologists who study earthquakes can determine when an
  earthquake started by noting the arrival times of P-waves and S-
 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

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?
• The epicenter is the point on the
  Earth’s surface directly above an
  earthquake’s starting point.
• The focus is the point inside the
  Earth where the earthquake begins.
• The epicenter is located directly
  above the focus.
 Measuring Earthquakes
• There are two major ways
  earthquakes are measured:
• 1. Richter Scale
• 2. Mercalli Scale
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
   8 or greater Great earthquake. Can cause serious damage in
    areas several hundred kilometers across.
    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
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
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
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
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.
                                      1. What was the
                                         magnitude of the
     Oahu                                earthquake?
                                      2. Where was the
              Maui V-VI                  intensity the
                             Hawaii   3.According to the
            6.7                          Mercalli Scale on
                  VII                    what island did the
                        VI     V         most damage
                                         likely occur?
Mercalli Intensity Scale
                1. What is the intensity at
                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
Earthquakes in Alabama?

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

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