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Primary and Secondary Waves. (“The Slinky”). An Overview of Seismic Waves. (“The Rope”). The Outline. The Types of Seismic Waves Seismic Wave Velocities P and S Wave Shadow Zones Seismographs P and S Waves Help Locate Earthquakes The S Wave and The Richter Scale Nuclear Testing

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primary and secondary waves

Primary and Secondary Waves

(“The Slinky”)

An Overview of Seismic Waves

(“The Rope”)

the outline
The Outline
  • The Types of Seismic Waves
  • Seismic Wave Velocities
  • P and S Wave Shadow Zones
  • Seismographs
  • P and S Waves Help Locate Earthquakes
  • The S Wave and The Richter Scale
  • Nuclear Testing
  • Conclusion
types of seismic waves
Types of Seismic Waves
  • Body waves: move through the earth

- P and S waves

  • Surface waves: travel near the earth’s surface
  • - Rayleigh and Love waves
types of seismic waves4
Types of Seismic Waves
  • Surface waves: trapped near the earth’s surface

Love wave: horizontal motion that is  to wave direction

Rayleigh wave: causes the ground to shake in elliptical motion, with no  motion

types of seismic waves5
Types of Seismic Waves
  • Body waves: move through interior of the earth

P wave: shakes the ground back and forth in same and opposite direction as the wave direction

S wave: shakes the ground back and forth  to wave direction

wave velocity
Wave Velocity
  • P waves: travel at 4-7 km/s
  • S waves: travel at 2-5 km/s

Blue primary waves followed by red secondary waves move outward in concentric circles from the epicenter of an earthquake off British Columbia and Washington State

wave velocity7
Wave Velocity
  • Differences in velocity allow mapping of the Earth’s interior
p wave shadow zone
P Wave Shadow Zone
  • P waves refract as they pass through the mantle-core boundary
  • Allows for better re-construction of Earth’s interior
s wave shadow zone
S Wave Shadow Zone
  • Leave a larger shadow zone
  • Allows for better re-construction of Earth’s interior
what s a seismograph
What’s a Seismograph?
  • Records P and S waves
  • Base and graph move with the ground
  • Mass and pen stay rigid
  • Record is called a seismogram
the 1 st seismograph
The 1st Seismograph?
  • Invented by Choko (136 C.E.)
  • Cu vessel with 8 dragon heads attached to it
  • Each holding balls in their mouths and 8 open-mouthed frogs directly below each one
today s seismograph
Today’s Seismograph
  • Called broadband because can sense ground motion over a wide range of frequencies
  • Measure amount of electrical energy needed to keep the mass centered
p s waves locate earthquakes
P & S Waves Locate Earthquakes
  • Measure the arrival time between P and S waves
  • At least 3 seismograms needed

Blue P waves followed by red S waves move outward in concentric circles from the epicenter of an earthquake off British Columbia and Washington State

the s wave and the richter scale
The S Wave and The Richter Scale
  • S wave amplitude determines the Richter Magnitude
  • Developed to make a quantitative measure of the relative sizes of earthquakes in S. Calif.
p s waves and nuclear testing
P & S Waves and Nuclear Testing
  • Underground nuclear explosions create P and S waves
  • Challenge: detect very small explosions
conclusion
Conclusion
  • P and S waves are a tool in locating quakes
  • “Harmless” compared to surface waves

- think “The Slinky” and “The Rope”

  • Better understanding of these seismic waves have resulted in more accurate maps of Earth’s interior
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