The waves propagate outwards as the reverberate, loose energy with distance, measurable as an absence of seismic readings between 104°-140°, and then combine at the other end of the planetary crust at 180° from the epicentre and therefore give off higher readings beyond the "shadow zone".

Note, a hollow Earth, as evident from seismographic data, does not necessarily mean that there is a hole at the poles, the animation below happened to be the best I could find.

So, the P and S waves in seismology are the same wave propagating in different directions.

The contemporary model to explain the seismic data, for comparison,

Dr. James Maxlow's expansion tectonics and a hollow Earth

It is known that the Earth's radius has increased 4-fold or so, evident from the oceanic crust that has formed as new crust while Earth has grown, the age of the oceanic crust being the youngest at the mid-oceanic rift zones, and the oldest close to the continents.

Since the Earth has grown, it is quite intuitive that it could be hollow, with a central "sun".

Dauvillier's idea of Pluto as the core of a former gas giant

Dauvillier suggested in 1951 that Pluto is the core of a former gas giant, solid iron, the end stage of the life cycle of a planet. That was later corroborated by that Pluto reflects light similar to iron (Manning, 1971). New Horizon's images, to me, seem to corroborate that hypothesis as well, an idea that is 70 years old at this point.

If Pluto is solid iron and the core of a former ice giant (and surrounded by the rest of that ice giant with the Kuiper belt), then we are lucky because we are able to see, optically, as in not just seismologically, the inside of a planet. Few people have considered that as far as I'm aware. The size of Pluto is around 2/3rd of our moon.

Synapses

Is Pluto an Iron-rich Planet? - nature.com (1971)

On The Origin of Pluto, Charon, and the Pluto-Charon Binary (1996)