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L19_SeismicRefractionII-page3

# L19_SeismicRefractionII-page3 - is the difference between...

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Applied Geophysics – Refraction II Phantom arrivals 1. Shoot a long-offset shot, S L 2. The head wave traveltime curves for both shots will be parallel, offset by time T 3. Subtract T from the S L arrivals to generate fictitious 2 nd layer arrivals close to S – the phantom arrivals 4. The intercept point at S can then be determined: T i 5. Use the usual formula to determine perpendicular layer thickness beneath S 1 2 2 1 2 2 2 V V V V h T s i = Applied Geophysics – Refraction II Separation of delay times Delay time is the difference between
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Unformatted text preview: is the difference between the slant path traveltime (AB) and the traveltime along the refractor beneath (A’B) Delay time below shotpoint S: 1 2 2 1 2 2 2 1 2 1 tan cos ' V V V V h T V i h i V h T V B A V AB T A S c A c A S S − = ∆ − = ∆ − = ∆ 1 2 2 1 2 2 V V V V h T D D − = ∆ Likewise, beneath D: The delay time is related to the perpendicular depth beneath the geophone. If we know the delay time, V 1 and V 2 then we can calculate the depth....
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