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

Source notation assumption: the second printed $V_{p3}=3000\mathrm{m}{\mathrm{s}}^{-1}$ is interpreted as $V_{s3}=3000\mathrm{m}{\mathrm{s}}^{-1}$. Otherwise the S-wave velocity in salt is not supplied, and this part and the salt S-wave calculations below would have no numerical answer. Retain the printed densities, including the unusually low salt value, rather than silently replacing them with typical rock properties.

With that interpretation, Snell law for elastic waves gives