Download - Surface Wave Dispersion
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Surface Wave Dispersion
James CraneBolu Owolana
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Outline
• Introduction• History• Concept• Examples• Conclusions
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Intro
• What is a surface wave• Types• Rayleigh waves are used for inversion
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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
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Concept
• Dispersion: waves spreading out at different velocities.
• Group vs. Phase velocity
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Group vs Phase velocity
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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
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Examples
• Earthquakes
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• Underwater explosions– Depth charges
set off – Noticed
dispersion on the pressure wave
– High frequency (short wavelength) arrived first indicating a high velocity
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• Submarine Geology – Bikini Atoll
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• Ground roll
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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.