A simple question about one seismogram can open the door into the wonderful world of wave propagation.
Core phases can sometimes look as simple as the teleseismic P waves.
However, the MichSeis and OhioSeis seismograms appeared quite complex with multiple pulses and odd emergent first arrivals from the Banda Sea event. Seismologists use a compact and efficient notation to designate body-wave arrivals, but there is some unfortunate confusion over the details of core phase identification. Raytracing plots of these core phases can be seen at the EduPhase Web site. If our Earth had no inner core, then the two branches of the PKP caustic structure would be the extent of core phases. As we follow the PKPbc branch out to larger distances, the PKPbc rays are bottoming more deeply into the core.