Sorry, that should've said SaberTooth's dream and 2sheep's images. Also, in reference to 2sheep's images, I don't really remember how subduction can occur in the Atlantic (thus sinking the East Coast) from geology class. Perhaps the East Coast can be pushed up into dramatic Himalayas overnight, but... *shrug*
Just something to keep in mind.
I suspect there are many ways that geology could move to result in sinking of land on the east coast.
Perhaps a huge new volcano off the coast somewhere? Unlikely probably but perhaps could be.
I suspect the mountain building sort of movements might be more likely.
God alone knows. We shall see.