Earthquakes and Seismic Waves

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Earthquakes and Seismic Waves
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Earthquakes and Seismic Waves

• Earthquake
• Shaking and trembling that results from the
  movement of rock beneath Earths surface.
• The forces of plate movement cause earthquakes.
• Stress increases along a fault until the rock
  breaks- resulting in an earthquake.

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Earthquakes and Seismic Waves
Building Damage
Road Damage
House Damage
Bridge Damage
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Earthquakes and Seismic Waves

• The focus is the area BENEATH Earths surface
  where rock that is under stress breaks
• The epicenter is the point on the SURFACE
  DIRECTLY ABOVE the focus.

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Earthquakes and Seismic Waves
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Earthquakes and Seismic Waves

• Seismic Waves
• Vibrations that travel through Earth
• Carry energy from an earthquake away from the
  focus, through the Earths interior, and across
  the surface.
• 3 main categories P waves, S waves and surface
  waves.

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Earthquakes and Seismic Waves

• Primary Waves (P waves)
• First waves to arrive
• Can travel through liquids AND solids
• Pushes and pulls materials as they move through
  earth
• 2 important terms to describe P waves
• 1. Compression The compressed part of the
  wave. Its the name of the region where the
  coils of the slinky are pushed together.
• 2. Rarefaction The spread out part of the
  wave. As the wave travels, rarefactions takes
  turns with compressions. Its the name of the
  region where the coils of the slinky are pulled
  apart.

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Earthquakes and Seismic Waves
http//www.edinformatics.com/math_science/transver
se_longitudinal_waves.htm
http//www.youtube.com/watch?v2rYjlVPU9U4
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Earthquakes and Seismic Waves

• Secondary Waves (S waves)
• S waves arrive second after P waves
• Travels through solids ONLY
• Vibrates side to side as well as up and down
• Shakes structures violently
• 3 important terms to describe S waves
• 1. Crest The highest part of an S wave.
• 2. Trough The lowest part of an S wave.
• 3. Amplitude the distance from the middle of
  the wave straight up to the top of a crest or
  straight down to the bottom of a trough

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Earthquakes and Seismic Waves
http//www.edinformatics.com/math_science/transver
se_longitudinal_waves.htm
http//www.youtube.com/watch?ven4HptC0mQ4
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Earthquakes and Seismic Waves

• Surface Waves
• Moves more slowly than P waves and S waves
• Produce severe ground movements
• Makes the ground roll like ocean waves.
• Shakes buildings from side to side.
• Most destructive

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Earthquakes and Seismic Waves

• P Waves go through solids and liquids
• S Waves go through solids ONLY

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Earthquakes and Seismic Waves

• Measuring Earthquakes
• Magnitude is a number that geologists assign to
  an earthquake based on the earthquakes size.
• Geologists determine magnitude by measuring the
  seismic waves and fault movement.
• 2 ways of measuring earthquakes Richter Scale
  and Mercalli Scale

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Earthquakes and Seismic Waves

• Richter Scale
• Rating of an earthquakes magnitude based on the
  size of the earthquakes seismic waves.
• Here, the waves are measured by a seismograph
• Provides accurate measurements for small, nearby
  earthquakes
• Does not work well for large or distant
  earthquakes

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Earthquakes and Seismic Waves

• Mercalli Scale
• Rates earthquakes according to the level of
  damage
• 12 steps that describe an earthquakes effects
• same earthquake can have different ratings due to
  different amounts of ground motion at different
  locations.
• Uses Roman numerals to rank how much damage is
  caused

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Earthquakes and Seismic Waves

• Locating the Epicenter
• Geologists use seismic waves to locate the
  epicenter
• P waves arrive at a seismograph station first,
  with S waves following second
• The difference between the arrival time of P
  waves and S waves is measured
• Geologists draw three circles using data from
  different seismographs stations.
• The center of each circle is the seismograph
  stations location
• The radius of each circle is the distance from
  that seismograph station to the epicenter
•  

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Earthquakes and Seismic Waves
Look at the diagram below the point where the
three circles intersect is the location of the
epicenter.
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Earthquakes and Seismic Waves
Where do you see the epicenter?
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Earthquakes and Seismic Waves
Where do you see the epicenter?
http//www.youtube.com/watch?v694yaY2ylTg
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Earthquakes and Seismic Waves

• Seismograph
• A device that records ground movements caused by
  seismic waves as they move through earth
• How does a Seismograph work?
• a heavy weight attached to a frame by wire
• A pen connected to the weight, rests its point on
  a rotating paper drum
• As the paper drum rotates slowly the pen draws a
  straight line
• Seismic waves cause the drum to vibrate, while
  the pens records the drums vibrations
• http//www.youtube.com/watch?v83GOKn7kWXM

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Earthquakes and Seismic Waves
This is what P waves, S waves and Surface waves
look like on a seismograph.