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Primary and Secondary Waves

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

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  1. Primary and Secondary Waves (“The Slinky”) An Overview of Seismic Waves (“The Rope”)

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. Wave Velocity • Differences in velocity allow mapping of the Earth’s interior

  8. P Wave Shadow Zone • P waves refract as they pass through the mantle-core boundary • Allows for better re-construction of Earth’s interior

  9. S Wave Shadow Zone • Leave a larger shadow zone • Allows for better re-construction of Earth’s interior

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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.

  15. P & S Waves and Nuclear Testing • Underground nuclear explosions create P and S waves • Challenge: detect very small explosions

  16. 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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