Lore:Pocket Guide to the Empire, 1st Edition/Cyrodiil - The Unofficial Elder Scrolls Pages (UESP)
The Greybeards speaking causes the world to shake. Todd Howard himself confirms this is literal.
http://www.gameinformer.com/themes/...im-s-dragon-shouts&GroupKeys=&PostPageIndex=1
The Greybeards...