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L19_SeismicRefractionII-page9

L19_SeismicRefractionII-page9 - Elastic moduli Poisson’s...

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Applied Geophysics – Refraction II Hidden layers Limitations If a layer is thin it may never produce a first arrival Lower layers always appear too shallow as a layer has been missed Either the direct or refraction from a lower (much higher velocity layer) is always first Applied Geophysics – Refraction II Velocity and rock strength Relating velocity to rock strength allows site classification based on refraction studies 1.
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Unformatted text preview: Elastic moduli: Poisson’s ratio ) ( 2 2 2 2 2 2 S P S P V V V V − − = σ • Tells us about the elastic strength of the material • Important for building foundations etc • Determined from knowledge of V P and V S – need shear sources and horizontal geophones for V S 2. Degree of jointing • Jointing lowers seismic velocity • Degree of jointing can be estimated from velocity for a known rock type...
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