Earthquakes

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Earthquakes
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What is an earthquake?
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An earthquake is

• The vibration of the earth caused by the sudden
  motion of tectonic plates
• Energy is transferred through the ground from
  the origin outward in a series of seismic waves
  through the earth

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Location of earthquake

• The point along the boundary where the plates
  begin to slip is called the Focus.
• This may not be on the surface
• The point on the surface directly above the foci
  is called the epicenter

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Earthquakes

• Occurs along faults), or fractures in the earth,
  between 2 sections of earth moving differently
• Only a portion of the boundary during any single
  earthquake

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Why do earthquakes occur?

• Because motion of tectonic plates is not constant
• Force has to build up to overcome friction
  between plates
• When applied force gt friction force between
  sections, an earthquake occurs

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Where do earthquakes occur?

• Earthquakes are normally near plate boundaries
• Any motion of plates can generate earthquakes
• Divergent boundaries
• Convergent boundaries
• Transform boundaries

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Faults around Southern California
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Why are all earthquakes not the same?
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What makes a difference between earthquakes?

• Related to the amount of force and energy
  associated with the movement of the plates at a
  boundary (transform, convergent more)
• Depends on the location where earthquakes
  originates in the earth (the focus). Deep focus
  earthquakes are less dangerous

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How long do quakes last?
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How long do quakes last?

• Small quakes last for less than 30 seconds
• Significant quakes between 30 seconds and 2
  minutes
• Major quakes upwards of 4 minutes

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What are aftershocks and are they dangerous?
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What are aftershocks?

• When one section of a plate boundary experiences
  an earthquake, the entire plate does not move.
• Those portion that do not originally move are
  placed under greater force (stress), which can
  result is subsequent earthquakes at other points
  along the boundary (fault line)

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Are aftershocks dangerous?

• They can be as strong as the original
• Buildings already weakened from the first may
  collapse after additional earthquakes

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How can an earthquake cause damage/harm?
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How can an earthquake cause damage/harm?

• Motion of buildings/bridges/roads causes collapse
  
• Rupture of gas/oil lines cause fires
• Falling glass, pieces of buildings
• Disruption of food/medical supply lines
• Loss of shelter
• Tsunamis along the coast for major earthquakes

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How can an earthquake cause damage/harm?
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How can an earthquake cause damage/harm?

• Motion of buildings/bridges/roads causes collapse
  
• Rupture of gas/oil lines cause fires
• Falling glass, pieces of buildings
• Disruption of food/medical supply lines
• Loss of shelter
• Tsunamis along the coast for major earthquakes

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Liquefaction

• When the ground becomes liquid-like during an
  earthquake
• Buildings sink and landslides result from this

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Tsunamis

• Great wave
• Much wider than a regular wind driven wave
• Caused primarily by undersea earthquakes,
  landslides, water must be displaced

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How are earthquakes measured?
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How are earthquakes measured?

• A scale based on the energy released by an
  earthquake was developed.
• Named after its creator, Richter
• Another scale based on damage done was developed
• Named after its creator, Mercalli

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Richter is most reported

• Logrithmic in nature, therefore doubling the
  value more than doubles the energy
• Under 4, not felt by humans
• 4-5.5 are significant earthquakes,that cause
  minor damage in 1st world countries, major damage
  in 3rd world countries

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Richter scale

• 5.5 8 major earthquake, can cause significant
  damage
• 8 9.5 once in a generation quake, major damage
• gt9.5 wow, run for the hills (if they are still
  there)

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Recording an Earthquake
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Seismograph
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What is used to record an Earthquake?

• Seismogram
• Converts the motion of the ground (energy waves
  into a visual graph
• Different waves are created by an earthquake

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Wave Types shown on a seismograph

• P waves (compression waves)
• Fastest
• S waves (transverse waves)
• Mid Speed
• Surface waves
• Slowest, may not reach far from epicenter

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