Earthquake Unit: Lesson 2

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Earthquake Unit Lesson 2

• Recording Earth Quakes and Seismic Waves

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Vocabulary

• Seismic Wave An elastic wave generated by an
  impulse such as an earthquake or an explosion.
  Seismic waves may travel either along or near the
  earths surface or through the earths interior.
• Seismograph detects and records seismic waves.
  Records the vertical and horizontal motions of
  the earth, by tracing wave shaped lines on paper
  or by translating the motion into electronic
  signals

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Primary Waves or P-waves

• Fastest moving waves
• First to be recorded by a seismograph
• P waves can travel through solids and liquids
• More rigid the material the faster the P waves
  travel
• Cause rock particles to move together and apart
  alone the direction of the waves

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Secondary waves or S-waves

• Second waves to be recorded
• Travel only through solid material
• Cause rock particles to move at right angles to
  the directions in which the waves are traveling
• Cannot be detected on the side of the earth that
  is opposite the earthquakes epicenter. Why?
• (Because they cannot travel through the liquid
  part of the earths outer core)
•  

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Long waves or L-waves

• Also called surface waves
• When p waves and s waves reach the earths
  surface their energy is converted into this type
  of wave
• Slowest moving waves
• Last to be recorded on a seismograph
• Travel slowly over the earths surface I a
  movement similar to that of ocean waves
• Cause the surface of the earth to rise and fall
  particularly destructive when traveling through
  loose earth

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Locating an Earthquake

• To find the epicenter of an earthquake scientist
  analyze the difference between the arrival times
  of the P waves and the S waves
• Scientist plot the difference in arrival time of
  the S and P waves called lag time
• Must plot the data from at least three different
  seismograph stations
• Compare the results and epicenter of the
  earthquake may now be located.

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Richter Scale

• Measures the magnitude of the earthquake
• Magnitude is the measure of the energy released
  by an earthquake.
• Largest earthquake so far had a magnitude of 9.6
• Major earthquakes have a magnitude of 7 or above
• Moderate earthquakes have a magnitude of between
  6 or 7
• Minor earthquakes have a magnitude of between 2.5
  and 6
• Micro quakes have a magnitude of less that 2.5
  and are usually not felt by people

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Mercalli scale

• Expresses the intensity of an earthquake
• The amount of damage it causes
• Measured in roman numerals from I to XII
• Ex. II-low intensity. Felt by only a few persons
  at rest. Delicately suspended objects may swing.
• Intensity X- some well built wooden structures
  destroyed. Most masonry and frame structures
  destroyed-foundations badly cracked
• Landslides, shifted sand and mud, water splashed
  over banks
• Intensity XII- total destruction

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Haiti Earthquake
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Earthquake in China
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Japan Earthquake
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Indonesia Earthquake
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Study or Quiz questions

• What instrument is used to record seismic waves?
• Explain the three types of seismic waves.
• How is the epicenter of an earthquake located?
• How do scientist measure the magnitude of an
  earthquake?
• Why do P waves travel faster through the
  lithosphere that through the asthenoshpere?