Seismic wave theory

i would like to hear the FE theory on seismic waves, and in turn tectonic plates (as i have read that at least a couple of you dont believe they exist)

the RE theory on waves is relatively simple, on a basic level atleast
this includes primary waves, secondary waves and surface waves

i am interested in how you would explain shadow zones and how particular waves can be detected from the direct other side of the world.
you might also note how these wave movements also show some pretty solid evidence of an outer core made of molten iron/nickel

I'll be keeping an eye on this one.  I think I've seen this asked before, but can't remember any answers.
Now then, as I am doing a degree in Geology, and as such have studied plate tectonics and seismic waves, I'll make sure to add my own opinion when I hear what FE'ers have to say.

Definitely expect a response from Raist on this one.

In FE, there'd be no (or few) problems with Surface, Love and Raleigh waves. It's the Primary and Secondary waves that give it trouble.

The density of the cores are the only major assumptions, but even then they have been calculated and peer reviewed, so are probably fairly close.  Once scientists figured out (don't ask me how...) the size/weight of the earth, they put in the densities of the crust and mantle (both of known density) and what was left must be the core.  Iron and Nickel seem to fit the data, and would also give the magnetic field around earth.

Seismics are often used to find densities of things, and map out locations when they are underground.  It's a well documented and reliable technique.  

I'm sure searching around could yield you some decent answers that people have had in the past. There was someone, although I can't recall who, that made a diagram to try and explain a possible way the waves would work.

what part doesn't work?

Largely, P and S wave shadow zones.  Plus, there may be problems with Surface wave propagation towards the South of a FE.  Also, the timing and recording of seismic waves might be a bit squiffy the further south you go.