Very large quakes, like those that occur at subduction zones where one tectonic plate slides under another, release powerful waves. Some of these so-called PKP waves travel through the mantle ...

Scientists were looking to examine how PKP waves caused by very large earthquakes could travel through the middle of Earth to the other side of the core through the mantle, the liquid outer core ...

The diagrams show what happens when P waves and S waves pass through the Earth. S waves do not pass through the Earth's core S waves cannot pass through the liquid outer core, but P waves can.