Past exam of the year 2 of the earth sciences (geology) course of the University of Oxford / 2022 / Paper 1 / 6 / c

At P critical incidence the transmitted P wave travels along the interface. The common horizontal seismic ray parameter is $1/V_{P2}$, givingThe resulting seismic head wave radiates back into the slower upper layer.

For a converted lower-layer S wave head wave, set the transmitted S angle to $90^{\circ }$:This is possible because $V_{S2}>V_{P1}$. It is the incident P angle needed for the converted SV branch to become tangential, not an S incident angle in layer 1.