= Solution
For the ray sketches in (i) and (ii), take a horizontally layered isotropic medium, a surface source and receiver, depth $z$ positive downwards, and <wave speed> $v(z)$. <Snell's law> conserves $p=\sin i/v$, where $i$ is measured from the vertical. A returning diving ray turns where $pv(z_t)=1$, with
$$
X(p)=2\int_0^{z_t}\frac{pv(z)}{\sqrt{1-p^2v(z)^2}}\,dz,\qquad
T(p)=2\int_0^{z_t}\frac{dz}{v(z)\sqrt{1-p^2v(z)^2}},\qquad \frac{dT}{dX}=p.
$$
For a uniform positive <gradient> $v=v_s+\beta z$, rays are <circular arcs> and
$$
X=\frac2\beta\sqrt{v_t^2-v_s^2},\qquad
T=\frac2\beta\operatorname{arcosh}(v_t/v_s)
=\frac2\beta\operatorname{arsinh}\!\left(\frac{\beta X}{2v_s}\right).
$$
Thus ordinary <travel time> increases with distance but has a decreasing slope as deeper rays sample faster material. The following two leaves discuss the labelled changes to this reference structure.
For the \b[OR alternative, the supplied fault-plane diagrams], assume the usual convention that shaded quadrants are compressional first motions on a lower-hemisphere projection. Each pair of nodal planes represents a <fault plane> and an auxiliary plane; first-motion polarity alone cannot choose which slipped. Geological mapping, <aftershock> locations or rupture observations can resolve that ambiguity.<Focal mechanisms or beachballs by United States Geological Survey>[Lower-hemisphere projection, compression shading and two possible fault planes]{ref}
\b[Diagram (i): <normal faulting>.] The central unshaded band indicates the extensional dip-slip pattern. It is compatible with crustal extension, such as a continental rift or a spreading environment, with a hanging wall moving down relative to the footwall on the actual fault. Its two curved nodal traces are the possible fault and auxiliary planes.
\b[Diagram (ii): <strike-slip faulting>.] The two straight nodal diameters divide four alternating quadrants, as expected for two vertical candidate planes. It is compatible with a transform plate boundary or continental shear zone. One candidate is right lateral and the conjugate is left lateral; polarity alone does not select the actual plane. Without a north arrow, geographical strikes cannot be assigned.
\b[Diagram (iii): <oblique-slip faulting> with a reverse component.] The off-centre nodal intersection and curved traces distinguish it from pure vertical strike slip, while shading through the centre indicates the reverse component under the stated convention. It is compatible with <transpression>, such as oblique convergence at a plate margin or a compressional strike-slip bend. Both strike-slip and dip-slip components are required; it is not merely a rotated pure strike-slip pattern. Exact strike, dip, rake, and slip-plane selection cannot be recovered numerically from this uncalibrated printed sketch. Reversing the shading convention would reverse the normal/reverse interpretation, so the convention is essential.
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