L19_SeismicRefractionII-page5 - The plus-minus method...

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Applied Geophysics – Refraction II The plus-minus method Given the delay time T D , (from the “plus”) and the velocities V 1 (from direct arrival) and V 2 (from the “minus) We can calculate the perpendicular depth: 1 2 2 1 2 2 V V V V h T D D = Note: we need to see refracted arrivals from both forward and reverse shots (three geophones only in figure) Use long offset shots to collect necessary data for all geophones Applied Geophysics – Refraction II
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Unformatted text preview: The plus-minus method Assumptions and approximations 1. The relief on the refractor must be small compared to the depth 2. Geometric relations assume a small refractor dip (dip < 10 deg) 3. Refractor assumed to be planar between the two points of emergence to a given geophone (ie between C and E) So that ∆ T D is equal when shooting from both sides...
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