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Surface Wave Dispersion

Surface Wave Dispersion. James Crane Bolu Owolana. Outline. Introduction History Concept Examples Conclusions. Intro. What is a surface wave Types Rayleigh waves are used for inversion. History. Earliest theoretic study of dispersion was made by Love.

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Surface Wave Dispersion

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  1. Surface Wave Dispersion James Crane Bolu Owolana

  2. Outline • Introduction • History • Concept • Examples • Conclusions

  3. Intro • What is a surface wave • Types • Rayleigh waves are used for inversion

  4. History • Earliest theoretic study of dispersion was made by Love. • Many years later Lord Rayleigh worked out the theory of wave propagation along free surface with retrograde elliptical motion http://slam.asu.edu/images/seismogram.gif

  5. Concept • Dispersion: waves spreading out at different velocities. • Group vs. Phase velocity

  6. Group vs Phase velocity

  7. Dispersion • Phase/group velocities vary with wavelength • Can be used to evaluate subsurface characteristics because the depth of investigation is wavelength dependent • longer wavelengths reflect the depths to which they travel • Shorter wavelengths provide crucial information about the shallow subsurface

  8. Examples • Earthquakes

  9. Underwater explosions • Depth charges set off • Noticed dispersion on the pressure wave • High frequency (short wavelength) arrived first indicating a high velocity

  10. Submarine Geology – Bikini Atoll

  11. Ground roll

  12. Conclusion • Surface waves are useful in determining velocity, density, elastic properties. • Surface waves can be a useful by-product of seismic exploration rather than a waste product.

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