Earths Interior

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Earths Interior

• Earthquakes
• Volcanoes

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What are Earthquakes?

• Seismology the study of earthquakes
• Where do Earthquakes occur?
• Fault a break in the Earths 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.

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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 deform.
• 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

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Are ALL Earthquakes the same?
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How do Earthquakes travel?

• Seismic Wave waves of energy that travel
  through the Earth
• Body waves seismic waves that travel through
  the Earths interior
• 2 types of Body Waves
• P waves or Primary Waves travel through solids,
  liquids, and gases are the fastest seismic waves
• 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

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Locating Earthquakes

• Seismographs instruments located at or near the
  surface of the Earth that record seismic waves
• 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 earthquakes start time by
  comparing seismograms and noting the difference
  in arrival times of P waves and S waves

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Where did it happen?

• Epicenter the point on the Earths surface
  directly above an Earthquakes starting point
• Focus point inside the Earth where an
  earthquake begins
• Most common method to finding an Earthquakes
  Epicenter S-P time method.
• http//ve.ou.edu/weaver/eq_locating/locating.html

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Discoveries of Earths Interior

• 1. Moho marks the boundary between the Earths
  crust and mantle
• 2. Shadow Zone an area on the Earths 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 sulfur

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• Earthquake Hazard measures how prone an area is
  to experiencing earthquakes in the future.
• An areas 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/

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Modified Richter Scale
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Worldwide Earthquake Frequency(Based on
Observations Sine 1900)
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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 buildings 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-investiga
  ting-earthquakes-seismic-wave-protection-video.htm
  
• http//videos.howstuffworks.com/hsw/9216-investiga
  ting-earthquakes-earths-moving-crust-video.htm

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Are you prepared for an Earthquake?

• Before the Shaking Starts
• Safeguard your house against earthquakes
• Put heavier objects on lower shelves
• Reinforce your homes 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

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• Volcano a mountain that forms when molten rock,
  called magma, is forced to the Earths 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/vtypesvo
  lcan1.html

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• 3 basic features that volcanoes share
• 1. Lava/Magma hot liquid material, driving
  force
• 2. Vents holes in Earths 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

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• What erupts from a volcano?
• Non explosive produces mostly lava
• Explosive produces pyroclastic material
  consists of rock fragments created by explosive
  volcanic eruptions

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• 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

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Blocky Lava
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Pahoehoe
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Aa
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Pillow Lava
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• 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 air
• 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/Tep
  hra.html
• What are some major problems with these types of
  pyroclastic material?

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• 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 valleys
• 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.

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• 3 Basic Types of Volcanoes
• 1. Shield Volcanoes built out of layers of
  lava from repeated non explosive eruptions
• EX. Hawaiis, 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

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• The Formation of Magma
• Volcanoes form by the eruption of lava and
  pyroclastic material onto the Earths surface
• Volcanoes begin when magma collects in the deeper
  regions of the Earths crust and in the uppermost
  layers of the mantle, the zone of intensely hot
  and pliable rock beneath the Earths 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

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• Where do volcanoes form?
• Tectonic plate boundaries are likely places for
  volcanoes to form. The Ring of Fire contains
  nearly 75 of the worlds active volcanoes on
  land.
• http//www.crystalinks.com/rof.html
• http//www.acleanerenvironment.com/platetectonicno
  tes.html