= Solution
Choose using target depth, scale, expected contrasts, overburden, noise and required result. A \b[<seismic reflection survey>] uses reflected travel times and <amplitudes> to image interfaces; it needs useful <acoustic impedance> contrasts, sufficient bandwidth, suitable offsets and dense coverage for <moveout correction>, stacking and <seismic migration>. A large clay-cap/igneous contrast gives a potentially strong reflection here, but fractures, scattering and attenuation can obscure coherent events. At $100$ Hz the nominal quarter-wavelength <vertical seismic resolution> is about $3.75$ m in the claystone and $8.75$ m in the igneous rock, if that <frequency> reaches the target.
A \b[<seismic refraction survey>] uses first arrivals and critically refracted waves to estimate velocities and interface structure. The increase from $1500$ to $3500\,\mathrm{m\,s^{-1}}$ is favorable for a cap-base head-wave branch, provided the spread reaches sufficient offsets. Refraction/tomography may better constrain lateral velocity variations and fractures, but simple head-wave inversion can miss a low-velocity layer or a thin hidden layer and often has poorer boundary detail.
Use expected reflector continuity, velocity inversions, required aperture, access, near-surface complexity and cost to choose or combine the surveys. A pilot gather and travel-time modelling can test which phases will be measurable; the supplied velocities alone do not specify the reservoir depth or the best acquisition geometry.
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