Unit 3 – Earth s Interior by fjwuxn


									Earth’s Interior
      What are Earthquakes?
• Seismology – the study of earthquakes

• Where do Earthquakes occur?
   Fault – a break in the Earth’s crust along which blocks
    of the crust slide relative to one another

   Faults occur in many places, but they are especially
    common near the edges of tectonic plates where they
    form the boundaries along which the plates move.
    What causes Earthquakes?
 As tectonic plates push, pull or scrape against each
  other, stress builds up along faults near the plates edges
  and causes stress on the rocks, which causes plates to

 Deformation – the change in the shape of rock in
  response to stress.
    2 ways of rock deformation:
      1. Plastic deformation – acts like clay (can mold
        easy), but does not lead to earthquakes
      2. Elastic deformation – acts like a rubber band,
        and does lead to earthquakes
 Elastic Rebound – sudden return of elastically deformed
  rock to its original shape
         Are ALL Earthquakes the same?

    Plate Motion           Prominent Fault      Earthquake
                               Type            Characteristics

Transform – occurs      Strike-slip fault    Moderate, shallow
where two plates slip
past each other

Convergent – occurs   Reverse fault          Strong, deep
where two plates push

Divergent – occurs      Normal fault         Weak, shallow
where two plates pull
away from each other
           How do Earthquakes travel?

•    Seismic Wave – waves of energy that travel through
     the Earth
•    Body waves – seismic waves that travel through the
     Earth’s interior
     2 types of Body Waves:
    1. P waves or Primary Waves – travel through solids,
        liquids, and gases; are the fastest seismic waves
    2. S waves or Secondary Waves – 2nd fastest, but
        cannot travel through the entire Earth, like P waves
•    Surface Waves – move the ground much like ocean
     waves move water particles; cause the most damage
     during an earthquake
               Locating Earthquakes

• Seismographs – instruments located at or near
  the surface of the Earth that record seismic
• Seismogram – a tracing of earthquake motion
  created by a seismograph

• When did it happen?
   An earthquakes starts when rock slips suddenly
    enough along a fault to create seismic waves.
   Seismologists find an earthquake’s start time by
    comparing seismograms and noting the difference in
    arrival times of P waves and S waves
               Where did it happen?

• Epicenter – the point on the Earth’s surface directly
  above an Earthquake’s starting point
• Focus – point inside the Earth where an earthquake

• Most common method to finding an Earthquake’s
  Epicenter: S-P time method.
• http://ve.ou.edu/weaver/eq_locating/locatin
            Discoveries of Earth’s Interior

• 1. Moho – marks the boundary between the Earth’s
  crust and mantle

• 2. Shadow Zone – an area on the Earth’s surface where
  not direct seismic waves from a particular earthquake
  can be detected

• 3. Solid Inner Core – made mostly of iron, with some
  nickel, and smaller amounts of oxygen, silicon, and
• Earthquake Hazard – measures how prone an area is to
  experiencing earthquakes in the future.

• An area’s earthquake hazard level is determined by past
  and present seismic activity.

• West Coast – has a very high earthquake hazard level
  because it has a lot of seismic activity
• Gulf Coast and Midwest – have much lower earthquake
  hazard levels because they do not have as much
  seismic activity.
• http://earthquake.usgs.gov/recenteqs/
            Modified Richter Scale

Magnitude      Estimated Effects      Energy (Multiply by
                                      31.7 each unit
                                      higher) (**Examples)
2.0            Can be detected only   1
               by seismograph
3.0            Can be felt at         31.7
4.0            Felt by most in the    1,004.89
5.0            Causes damage at       31.855.013
6.0            Causes widespread      1,009,803.9
7.0            Causes great,          32,010,784
               widespread damage
            Worldwide Earthquake Frequency
           (Based on Observations Sine 1900)

Descriptor          Magnitude        Average Occurring
Great               8.0 and higher   1

Major               7.0 – 7.9        18

Strong              6.0 – 6.9        120

Moderate            5.0 – 5.9        800

Light               4.0 – 4.9        About 6,200

Minor               3.0 – 3.9        About 49,000

Very Minor          2.0 – 2.9        About 365,000
                       Earthquakes and Buildings

•   Modern Technology used to design and construct buildings and bridges to help
    withstand earthquakes.
      1. Mass Damper – a weight placed in the roof of a building. Motion sensors detect building
       movement during an earthquake and send messages to a computer. The computer signals
       controls in the roof to shift the mass damper to counteract the building’s movement.

      2. Cross-braces – are placed between floors and they counteract pressure that pushes and
       pulls at the side of a building during an earthquake.

      3. Active Tendon System – sensors notify a computer that the building is moving, then the
       computer activates devices to shift a large weight to counteract the movement.

      4. Flexible pipes – help prevent water and gas lines from breaking. They are better able to
       twist and bend without breaking during an earthquake.

      5. Base isolators – act as shock absorbers during an earthquake. Absorb seismic waves,
       preventing them from traveling through the building.

   http://videos.howstuffworks.com/hsw/9217-investigating-earthquakes-seismic-wave-
   http://videos.howstuffworks.com/hsw/9216-investigating-earthquakes-earths-moving-crust-
         Are you prepared for an Earthquake?

• Before the Shaking Starts:
    Safeguard your house against earthquakes
        Put heavier objects on lower shelves
        Reinforce your home’s structure
        Store nonperishable food, water, a fire extinguisher, a flashlight with
         batteries, and a first aid kit

• When the Shaking Starts:
    1. If indoors – crouch or lie face down under a table or desk
    2. If outdoors – lie face down away from buildings, power lines, trees
     and cover your head with your hands
    3. If in a car – stop the car and remain inside

• After the Shaking Stops:
    Remove yourself from immediate danger
• Volcano – a mountain that forms when molten rock,
  called magma, is forced to the Earth’s surface

• Two types of Eruptions:
    1. Non Explosive Eruptions
          Relatively calm outpourings of lava
          Release a huge amount of molten rock
    2. Explosive Eruptions
          Clouds of hot debris and gases shoot out from the volcano
          Can blast millions of tons of solid rock
          http://www.cotf.edu/ete/modules/volcanoes/vtypesvolcan
•   3 basic features that volcanoes share:
      1. Lava/Magma – hot liquid material, driving force
      2. Vents – holes in Earth’s crust where magma rises through
      3. Magma Chamber – stores magma inside volcano

•   Magma – the composition of the magma determines whether a volcanic
    eruption is non explosive, explosive or somewhere in between

•   Water – a volcano is more likely to erupt explosively, if its magma has a
    high water content

•   Silica
      Explosive eruption – the vents are plugged, causing a buildup of
         pressure and a massive explosion
      Non explosive eruption – the vents are not plugged
• What erupts from a volcano?
  Non explosive – produces mostly lava

  Explosive – produces pyroclastic material –
   consists of rock fragments created by
   explosive volcanic eruptions
• 4 Types of Lava
   1. Blocky Lava – usually oozes from a volcano,
    forming jumbled heaps of sharp edged chunks
   2. Pahoehoe (pah HOY hoy) – lava flows slowly, like
    wax dripping from a candle, forming a glassy surface
    with rounded wrinkles
   3. Aa (AH ah) – slightly stiffer lava that pours out
    quickly and forms a brittle crust
   4. Pillow Lava – forms when lava erupts underwater
Blocky Lava
Pillow Lava
• 4 Types of Pyroclastic Material
    1. Volcanic Blocks – largest pieces, consist of solid rock
     blasted from the volcano
    2. Volcanic Bombs – large blobs of magma that harden in the
    3. Lapilli (luh PILL ee) – pebble like bites of magma that
     become solid before they hit the ground
    4. Volcanic Ash – forms when the gases in stiff magma
     expand rapidly and the walls of the gas bubbles explode into
     tiny glasslike slivers

 http://www.geology.sdsu.edu/how_volcanoes_work/Tephra.html

 What are some major problems with these types of pyroclastic
• Major Problems with Volcanic Ash:
      1.   when mixed with water, has the same consistency as cement
      2.   can collapse buildings, due to weight
      3.   smothers crops
      4.   dams up rivers valley’s

• As the ash and gases spread around the globe, they can
  block out enough sunlight to cause the average global
  surface temperature to drop noticeable.

    EX. – Eruption of Mt. Pinatubo, in the Philippines caused an
     average global temperature to drop about 32.9* in 1991.
• 3 Basic Types of Volcanoes:
    1. Shield Volcanoes – built out of layers of lava from repeated
     non explosive eruptions
        EX. – Hawaii’s, Mauna Kea – tallest mountain on Earth, measured
         from the sea floor
    2. Cinder Cone Volcanoes – small volcanic cones made of
     pyroclastic material
        EX. – Paricutin, in Mexico
    3. Composite Volcanoes -- referred to as stratovolcanoes; form
     by explosive eruptions of pyroclastic material followed by quieter
     outpourings of lava
        EX. – Mt. Fuji, in Japan

• http://pubs.usgs.gov/gip/volc/types.html
• The Formation of Magma:
    Volcanoes form by the eruption of lava and pyroclastic material
     onto the Earth’s surface
    Volcanoes begin when magma collects in the deeper regions of
     the Earth’s crust and in the uppermost layers of the mantle, the
     zone of intensely hot and pliable rock beneath the Earth’s crust

 2 Factors the help form Magma:
    1. Pressure and Temperature – as pressure decreases and
     temp. increases magma is formed
    2. Density – once formed, magma rises toward the surface of
     the Earth because it is less dense than the surrounding rock
• Where do volcanoes form?
  Tectonic plate boundaries are likely places for
   volcanoes to form. The “Ring of Fire”
   contains nearly 75% of the world’s active
   volcanoes on land.


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