Question about S and P waves

[MattusMaximus]

Howdy all,

I recently got this question from a former student, and - not being a seismologist - I'm not quite sure how to address it:

Today in class I had a question concerning wave nature and my teacher wasn't able to answer it but I'm still curious so I was wondering if you would have any insight. We were discussing seismology and how P and S waves travel through the Earth and the differences between their actions, and since S waves cannot travel through liquid, they are said to simply "stop" at the outer core level. I was wondering if this means that the energy is simply absorbed by this layer or if the waves just reflect in a harmless manner, or if they are dissipated in another way. It is said that P waves are gradually refracted as they travel through all the core layers, but I can't find much info on S wave nature, especially after it hits the outer layer. Any thoughts you have would be much appreciated, especially since you're the physics god!

Any assistance would be appreciated, and I will promptly name you as one of my physics demigods

Cheers - MM

 

[Pulvinar]

Not a seismologist either, but conservation of energy says the S-waves must be being absorbed by the outer core since there's no reflection of them seen on the surface, just a shadow of that core. The energy would go into heating the outer core a little more. The matter is complicated though by some P-wave/S-wave mode conversion at interfaces.

 

[Slowvehicle]

Howdy all,

I recently got this question from a former student, and - not being a seismologist - I'm not quite sure how to address it:



Any assistance would be appreciated, and I will promptly name you as one of my physics demigods

Cheers - MM

Super simplified answer:
S waves are transverse waves (where particle displacement is perpendicular to wave direction). Since solids and liquids have different shear strengths, a transverse wave will not generally be transmitted across a solid/liquid interface. The energy of the transverse wave is scattered at that interface; some is absorbed by the medium, as heat, some is reflected, most is scattered (and eventually absorbed as heat).

Super simplified demo:
Put a piece of plywood in a swimming pool, perpendicular to the surface and parallel to an edge. If you move the plywood up-and-down ("establish a transverse wave") it will not make significant waves in the water; if you push the plywood back-and-forth (pull the flat side toward, then push it away from, the side of the pool , or "establish a longitudinal wave") it will cause significant waves in the water.

Extension: Consider what would change if the demo were performed in a pool of honey...

ETA: +1 what Pulvinar said...