 Solution

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

For the fully water-filled reservoir, the approximate densities and wave speeds give

Z_{p 2} ≃ 3.06 \times 1 0^{6}, Z_{s 2} ≃ 1.05 \times 1 0^{6} kg m^{- 2} s^{- 1},

and hence

R_{p} ≃ \frac{3.0625 - 2.25}{3.0625 + 2.25} ≃ + 0.15, R_{s} ≃ \frac{1.05 - 0.900}{1.05 + 0.900} ≃ + 0.08.

Both are positive: the reservoir has larger P wave and shear-wave impedances than the cap rock, and neither reflection reverses the chosen stress-wave seismic reflection polarity.

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