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Modes of Elastic Wave Propagation P-wave

Modes of Elastic Wave Propagation P-wave. http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm. Modes of Elastic Wave Propagation S-wave. http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm. Modes of Elastic Wave Propagation Rayleigh wave.

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Modes of Elastic Wave Propagation P-wave

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  1. Modes of Elastic Wave PropagationP-wave http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm

  2. Modes of Elastic Wave PropagationS-wave http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm

  3. Modes of Elastic Wave PropagationRayleigh wave http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm

  4. Modes of Elastic Wave PropagationLove wave http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm

  5. What does a seismic signal look like? • Broadband (short time) pulsed signal • Superposition of many sine waves with different amplitude and frequency From Dobrin and Savit, 1988

  6. Rayleigh Waves http://www.uwm.edu/~bketter/Research/Surface_Theory/Rayleigh/rayleigh_index.html

  7. Modes of wave propagation

  8. Location of Earthquakes • Hypocenter or earthquake focus • Epicenter • Earthquakes do not occur at points but occur due to stress release within small volumes or along fault planes

  9. Complications • Earth is not homogeneous or flat • P & S waves velocities are not constant • Earthquakes don’t normally occur at the surface • Errors in traveltime measurement • Precise solution requires many seismometers

  10. Earthquake location • Distance between epicenter and seismometer is called the epicentral distance • Shortest distance between two points on a sphere is along the great circle connecting those two points • Epicentral distance is the length of the great circle arc connecting the epicenter and seismometer • With measurement of ts-p can estimate epicentral distance with compilation of global traveltimes

  11. Classical Seismology • Global Seismology • Use energy released by earthquakes (or nuclear tests) to image Earth’s deep interior Source: http://www.mantleplumes.org

  12. Earthquake magnitude and moment • Concept of magnitude was first introduce by C.F. Richter in 1935 • Based on local earthquakes in Southern California • Based on amplitude of first arriving P-wave as measured on a particular seismograph (12Hz Wood-Anderson seismometer)

  13. Earthquake magnitude and moment • All magnitude scales are logarithmic and have the form

  14. Earthquake magnitude and moment • Shallow focus (<50km) teleseismic earthquakes (20°<Δ<160°)

  15. Earthquake magnitude and moment • Deep-focus earthquakes us P and S body waves – Gutenberg-Richter Scale (1956) • q~ 6: Δ=10°, ~6.5: Δ=80°, ~8: Δ=110° • Wordwide average of mb-MS

  16. Earthquake magnitude and moment • Seismic moment • Moment magnitude

  17. Identifying Seismic phases • P: P-wave in the mantle • S: S-wave in the mantle • K: P-wave in outer core • I: P-wave in inner core • J: S-wave in inner core • c: mantle outer core reflection • i: inner core outer core reflection • p: reflected P-wave close to focus from surface • s: reflected S-wave close to focus from surface • LR: Rayleigh Wave • LQ: Love Wave

  18. Identifying Seismic phases • PKP • PKIKP • PKJKP • PKiKP • sSP

  19. Identifying Seismic phases

  20. Identifying Seismic phases

  21. Identifying Seismic phases

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