[feynman]

As far as i know, i didn't saw a lot of FE geologist here... Each time someone is evocating the subject, FE moderators reply "we don't know about sismic reflexion sorry. But the fact is that if you said that it's impossible to go to space, a good way to prove the shape of the Earth would be by studying the intern structure right ? And i'm sorry to say that it has been done decades ago... And yes subduction IS proved by seismic tomography (at least it is the translation my poor english found for the world "tomographie sismique" in French). As you can't deny seisms, you can't deny the fact that the waves (S and P mainly) are travelling IN the "globe".
What do you reply to this pleeease ?

[Thork]

Earth is like a jaffacake.

Its flat, circular, has a gooey orange middle and a thin layer on the top. Why can't the chocolate layer be in the form of plates on a flat earth, moving over a delicious Jaffa mantle?

Why do you have to have a ball to have seismic waves? Imagine earth to be a bit like a tuning fork. You can have lots of shape and mass combinations and still ring the same note.

[feynman]

Why do you have to have a ball to have seismic waves?

Because there is a "shadow zone" with those waves and it can only be explained with a spherical earth. I'm sorry if all your theory is disprove by this but I can't really see how you can deny it (i'm studying geology by the way and i'm not part of any conspiracy)
http://www.emse.fr/~bouchardon/enseignement/processus-naturels/up1/web/la-terre-est-ronde/terre-ronde-geodynamique-0302-geophysique-seismicite_fichiers/image032.jpg