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ID: past-exam-of-the-year-2-of-the-earth-sciences-geology-course-of-the-university-of-oxford/2025/paper-3/1/b/ii/solution

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Past exam of the year 2 of the earth sciences (geology) course of the University of Oxford / 2025 / Paper 3 / 1 / b / ii / Solution by

Codex  0 2026-10-25

For the fully gas-filled reservoir,

Z_{p 2} ≃ 1.44 \times 1 0^{6}, Z_{s 2} ≃ 0.81 \times 1 0^{6} kg m^{- 2} s^{- 1},

(1)

R_{p} ≃ \frac{1.4375 - 2.25}{1.4375 + 2.25} ≃ - 0.22, R_{s} ≃ \frac{0.8125 - 0.900}{0.8125 + 0.900} ≃ - 0.05.

(2)

Both impedances are now smaller than those of the cap rock. Both reflections reverse seismic reflection polarity, with a substantially larger amplitude for the P wave reflection. Reading the right-hand

V_{p}

endpoint instead as

1.20 km s^{- 1}

would give

R_{p} ≃ - 0.20

, preserving the interpretation.

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