As a seismologist with extensive experience in the study of seismic waves, I can explain the behavior of S and P waves as they travel through the Earth's interior. P-waves, also known as primary waves, are compressional waves that can travel through solids, liquids, and gases. They are the fastest of the seismic waves and are the first to be detected by seismographs when an earthquake occurs. As P-waves travel through the Earth, they can pass through both the mantle and the core. However, when they reach the boundary between the mantle and the core, which is at a depth of about 2900 kilometers, they experience a change in speed and direction due to the difference in the properties of these two layers. This is known as refraction. S-waves, or secondary waves, are shear waves that move through solids by causing particles to move perpendicular to the direction of the wave's travel. Unlike P-waves, S-waves cannot travel through liquids. When S-waves encounter the liquid outer core, they are unable to pass through it and are instead absorbed. This inability of S-waves to travel through the outer core is a key piece of evidence that supports the theory that the outer core is indeed a liquid, as a solid would allow shear waves to pass through it. To summarize, P-waves can travel through both the mantle and the core but are slowed and refracted at the mantle/core boundary. S-waves, on the other hand, are absorbed at the mantle/core boundary because they cannot travel through the liquid outer core. read more >>

P-waves pass through both mantle and core, but are slowed and refracted at the mantle / core boundary at a depth of 2900 km. S-waves passing from the mantle to the core are absorbed because shear waves cannot be transmitted through liquids. This is evidence that the outer core does not behave like a solid substance.read more >>