Types of seismic waves

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Types of seismic waves

• Surface waves
• Rayleigh
• Love
• Body waves
• P waves
• S waves

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Surface waves

• Rayleigh up and down motion

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Surface waves

• Love waves side to side motion
• Causes damage to infrastructure

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Body waves

• P waves push and pull
• Compressional waves
• Travels through solid, liquid, and gas
• Travel 1.7 times faster than the S wave

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Body waves

• S waves
• Transverse waves
• Motion is perpendicular to wave propagation
• Travels only through solids

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Body waves in a seismogram
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P and S waves

• The difference in arrival times of P and S waves
  can be used to determine the distance of the
  earthquake.

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P and S waves

• Triangulation is used to determine the exact
  location of earthquake epicenters.

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Magnitude vs Intensity

• Magnitude the total amount of energy released
  during an earthquake
• Proposed by Charles Richter in 1935
• Measured 100 km as the standard distance
• Wood-Anderson instrument
• Objective means of measuring earthquakes

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Intensity

• Intensity - an indication of the destructive
  effects of an earthquake at a particular place
• Affected by factors such as
• Distance from epicenter
• Nature of underlying rock
• Quality of building materials
• Subjective means of measuring earthquakes
• Modified Rossi-Forrel scale

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Magnitude scale
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Effects of earthquakes

• During an earthquake, the region within 20-30 km
  of the epicenter ordinarily experiences the same
  degree of ground shaking.
• Changes only with differences in underlying rock
  type.

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Hazards associated with earthquakes

• Fire
• Landslides
• Ground subsidence
• Liquefaction
• Ground rupture
• Collapse of structures
• Tsunami

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Fire

• 1906 earthquake in San Francisco
• Most of the damage to S.F. was due to fire

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Landslide
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Ground subsidence
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Liquefaction
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Ground rupture
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Collapse of structures
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Tsunami
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Prediction of earthquakes

• Long-term prediction
• made possible through determination of active
  fault boundaries
• Seismic gaps

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Prediction of earthquakes

• Short-term prediction
• Abnormal emission of gases Radon (Ra230) from the
  decay of Uranium (Ur238)
• Swarms of tiny earthquake (foreshocks)
• Ground tilting uplift subsidence
• Measured by sensitive instruments (e.g. lasers,
  radar interferometry)

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Radar Interferometry
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