Past exam of the year 2 of the earth sciences (geology) course of the University of Oxford / 2023 / Paper 1 / 6 / q / Solution

Quality is degraded by vessel and flow noise, poor receiver coupling or position uncertainty, insufficient acquisition aperture and fold, coarse sampling and aliasing, and inaccurate source timing. Finite source bandwidth limits vertical seismic resolution; shallow-water reverberations, bubble pulses, source/receiver ghosts and seismic multiples overlap primary reflections. In $50\mathrm{m}$ of water with sound speed about $1500\mathrm{m}{\mathrm{s}}^{-1}$, the water-layer round-trip time is only about $0.067\mathrm{s}$.

Seismic attenuation removes high-frequency energy, geometric spreading weakens distant returns, and heterogeneous lithology, scattering and seismic anisotropy complicate travel paths and amplitudes. Incorrect seismic velocity models misplace reflectors during seismic migration; dipping structure and out-of-plane arrivals particularly challenge two-dimensional processing. Thin layers can cause wavelet interference and tuning. Finally, even noiseless data cannot recover a normal-incidence P reflection from the stipulated zero-contrast sandstone–salt boundary: that is absent signal rather than poor recording.