Seismic ray-path phase notation: uppercase letters (P, K, I) denote transmission/refraction through a boundary into a new medium, while lowercase letters (p, s, i, c) denote reflection off a boundary (surface, ICB, or CMB respectively).
For pPKiKP: the initial 'p' is a surface reflection near the source, 'PKiKP' involves refraction into the outer core (K) at the CMB, reflection off...
Full option-by-option analysis available to enrolled students.