Earthquakes, the Earths Interior

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Earthquakes, the Earths Interior Tsunamis

• 2.04a Analyze the seismic waves including
  velocity and refraction to
• Infer Earths internal structure
• Locate earthquakes epicenters
• Measure earthquake magnitude
• Evaluate the level of seismic activity in NC

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Todays Plan

• Introduction to the Earths Interior and
  Earthquakes.
• Video Questions
• Describe how the meeting of two tectonic plates
  can lead to an earthquake.
• Where does the greatest damage occur during an
  earthquake?

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What are Earthquakes?

• The shaking or trembling caused by the sudden
  release of energy
• Usually associated with faulting or breaking of
  rocks
• Continuing adjustment of position results in
  aftershocks

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What is the Elastic Rebound Theory?

• Explains how energy is stored in rocks
• Rocks bend until the strength of the rock is
  exceeded
• Rupture occurs and the rocks quickly rebound to
  an undeformed shape
• Energy is released in waves that radiate outward
  from the fault

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• The Focus and Epicenter of an Earthquake

• The point within Earth where faulting begins is
  the focus, or hypocenter
• The point directly above the focus on the surface
  is the epicenter

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• Seismographs record earthquake events

At convergent boundaries, focal depth increases
along a dipping seismic zone called a Benioff zone
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Where Do Earthquakes Occur and How Often?

• 80 of all earthquakes occur in the
  circum-Pacific belt
• most of these result from convergent margin
  activity
• 15 occur in the Mediterranean-Asiatic belt
• remaining 5 occur in the interiors of plates and
  on spreading ridge centers
• more than 150,000 quakes strong enough to be felt
  are recorded each year

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The Economics and Societal Impacts of EQs
Damage in Oakland, CA, 1989

• Building collapse
• Fire
• Tsunami
• Ground failure

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What are Seismic Waves?

• Response of material to the arrival of energy
  fronts released by rupture
• Two types
• Body waves
• P and S
• Surface waves
• R and L

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Body Waves P and S waves

• Body waves
• P or primary waves
• fastest waves
• travel through solids, liquids, or gases
• compressional wave, material movement is in the
  same direction as wave movement
• S or secondary waves
• slower than P waves
• travel through solids only
• shear waves - move material perpendicular to wave
  movement

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Surface Waves R and L waves

• Surface Waves
• Travel just below or along the grounds surface
• Slower than body waves rolling and side-to-side
  movement
• Especially damaging to buildings

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How is an Earthquakes Epicenter Located?

• Seismic wave behavior
• P waves arrive first, then S waves, then L and R
• Average speeds for all these waves is known
• After an earthquake, the difference in arrival
  times at a seismograph station can be used to
  calculate the distance from the seismograph to
  the epicenter.

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How is an Earthquakes Epicenter Located?
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How is an Earthquakes Epicenter Located?

• Time-distance graph showing the average travel
  times for P- and S-waves. The farther away a
  seismograph is from the focus of an earthquake,
  the longer the interval between the arrivals of
  the P- and S- waves

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How is an Earthquakes Epicenter Located?

• Three seismograph stations are needed to locate
  the epicenter of an earthquake
• A circle where the radius equals the distance to
  the epicenter is drawn
• The intersection of the circles locates the
  epicenter

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How are the Size and Strength of an Earthquake
Measured?

• Intensity
• subjective measure of the kind of damage done and
  peoples reactions to it
• isoseismal lines identify areas of equal intensity

• Modified Mercalli Intensity Map
• 1994 Northridge, CA earthquake, magnitude 6.7

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How are the Size and Strength of an Earthquake
Measured?

• Magnitude
• Richter scale measures total amount of energy
  released by an earthquake independent of
  intensity
• Amplitude of the largest wave produced by an
  event is corrected for distance and assigned a
  value on an open-ended logarithmic scale

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What are the Destructive Effects of Earthquakes?

• Ground Shaking
• amplitude, duration, and damage increases in
  poorly consolidated rocks

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Can Earthquakes be Predicted?

• Earthquake Precursors
• changes in elevation or tilting of land surface,
  fluctuations in groundwater levels, magnetic
  field, electrical resistance of the ground
• seismic dilatancy model
• seismic gaps

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Can Earthquakes be Predicted?

• Earthquake Prediction Programs
• include laboratory and field studies of rocks
  before, during, and after earthquakes
• monitor activity along major faults
• produce risk assessments

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Can Earthquakes be Controlled?

• Graph showing the relationship between the amount
  of waste injected into wells per month and the
  average number of Denver earthquakes per month
• Some have suggested that pumping fluids into
  seismic gaps will cause small earthquakes while
  preventing large ones

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Inside the Earth
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Composition (What it is made of)

• Crust
• Mantle
• Core

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The Crust

• Outer layer
• 5-100 km thick
• 2 types of crust
• Oceanic (very dense, made of basalt)
• Continental (less dense, made of granite)

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Oceanic and Continental Crust
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The Mantle

• Middle layer
• Very thick layer

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The Core

• Made mostly of iron
• 1/3 of the earths mass
• Very hot

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Earths Layers

• How are the earths layers similar to an egg?
• Shellcrust
• Egg whitemantle
• Yolkcore

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Physical Structure of the Earth(5 Layers)

• Lithosphere- rigid outer layer (crust)
• Asthenosphere- solid rock that flows slowly (like
  hot asphalt)
• Mesosphere- middle layer
• Outer Core- liquid layer
• Inner Core- solid, very dense

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Tectonic Plates

• Earths crust is broken into about 19 pieces
• These plates move on top of the asthenosphere

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Tsunami!

• What happened why

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2004 Indian Ocean Earthquake

• Undersea earthquake
• Magnitude 9.0 (Moment magnitude scale)

NOAA
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Epicenter 150 KM west of Sumatra
http//en.wikipedia.org/wiki/2004_Indian_Ocean_ear
thquake
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Occurred along the subduction zone where the
Indian dives under the Eurasian Plate
http//www.nps.gov/prsf/geology/images/plates.gif
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Facts

• The earthquake came just three days after a
  magnitude 8.1 earthquake in an uninhabited region
  west of New Zealand
• Possible connection between these two earthquakes
  
• Possibility of a seismic chain reaction across
  neighboring plates has also been considered

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Facts

• Total energy released by a magnitude 9.0
  earthquake exceeds the total amount of energy
  consumed in the U.S. in one month
• Massive release of energy and shift in mass
  insignificantly altered the Earth's rotation

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A tsunami (pronounced soo-NAA-mee) is a series of
waves (called a "wave train") generated in a body
of water by a pulsating or abrupt disturbance
that vertically displaces the water column.
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Tsunami's are also mistakenly referred to as
tidal waves as they often resemble a tide that
keeps rising, rather than cresting waves when
they reach shore. However, as they are not
actually related to tides the term may be
misleading, and its use is discouraged by
scientists.
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• Tsunamis are created when
• Seafloor quickly changes shape
• Water is displaced
• Waves are formed as the displaced water mass,
  which is affected gravity, tries to move back

Anthony Liekens 1530, 28 Dec 2004 (UTC)
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(No Transcript)
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Characteristics

• Move at high speeds
• Can travel enormous distances with little energy
  loss
• Can cause damage thousands of miles from its
  origin
• May be several hours between its creation and its
  impact on the coast

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Warning Systems
Many countries around the Pacific, including
Hawaii, have warning systems and evacuation
procedures in the event of a serious tsunami.
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Effects of Tsunamis

• Destruction of human life (100,000)
• Destruction of property
• Spread of disease
• Destruction of ecosystems

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