Earthquakes and earthquake or seismic waves

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Earthquakes and earthquake (or seismic) waves

• Pages 332-333, 338-341, 358-361

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EARTHQUAKE Vibrations caused by the sudden
release of energy stored in the rocks (page 332)
SEISMIC WAVES or EARTHQUAKE WAVES Energy that
moves through the earth because of an earthquake
(page 332)
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PROPERTIES OF WAVES In a uniform medium, a wave
radiates outwards as concentric spheres at
constant velocity Velocity of a wave depends on
the nature of the medium When a wave passes from
one medium to another, it refracts (bends) and/or
reflects (page 358)
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Surface waves
Travel along the surface of the earth
There are two broad groups of seismic waves (page
338)
Body waves
Can travel through the interior of the earth
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Body waves are used to study the internal
structure of the earth (pages 358-359)
Two different types of body waves (page 338)
PRIMARY or COMPRESSIONAL waves (P-waves)
SECONDARY or SHEAR waves (S-waves)
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http//web.ics.purdue.edu/braile/edumod/waves/Wav
eDemo.htm
Compressional Wave (P-Wave) Animation
Deformation propagates. Particle motion consists
of alternating compression and dilation.
Particle motion is parallel to the direction of
propagation (longitudinal). Material returns to
its original shape after wave passes.
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http//web.ics.purdue.edu/braile/edumod/waves/Wav
eDemo.htm
Shear Wave (S-Wave) Animation
Deformation propagates. Particle motion consists
of alternating transverse motion. Particle
motion is perpendicular to the direction of
propagation (transverse). Transverse particle
motion shown here is vertical but can be in any
direction. However, Earths layers tend to cause
mostly vertical (SV in the vertical plane) or
horizontal (SH) shear motions. Material returns
to its original shape after wave passes.
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• P-waves are faster than S-waves

• Both P-and S- waves travel faster through denser
  material

• Only P-waves can travel through liquids

• P- waves travel faster through solids than
  through liquids

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S-waves do not pass through the outer core
Figure on page 359
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P-waves can pass through parts of the core
Figure on page 359
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The instrument used to record an earthquake
Seismograph (page 339)
The actual record of an earthquake
Seismogram
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(Page 341)
Amplitude
Seismograms record the AMPLITUDE (height of the
peaks) of the seismic waves against TIME along
the horizontal axis
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What is the maximum amplitude recorded on this
seismogram?
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What is the maximum amplitude recorded on this
seismogram?
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RICHTER MAGNITUDE SCALE Specifies the amplitude
of the largest ground motion generated by the
earthquake at a seismograph station located 100
km from the epicenter
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Characteristics of Richter Scale

• The amplitude can be measured directly from a
  seismogram (more quantitative)
• The scale is logarithmic (page 341)
• An increase of one magnitude on the Richter scale
  means approximately 30- fold increase in energy
  released (page 341)