I didn't communicate my thoughts very well.
Water, due to the force of gravity, always seeks the LOWEST POINT. The surface of the ocean , on a global scale, is smooth and flat. The land, is not, and is subject to constant CHANGE.
There are continents where the 'sea level' is rising on one coast, while lowering on the other.
Imagine laying out a large plastic dropcloth, leaving lots of 'lumps' in it. Then poor water around on it.
Now, pull on the edges of the dropcloth.
Is the water rising/falling, or is it the 'ground' moving that causes the APPARENT change in sea level?
underwater structures which are solid, all in place, no earthquake damage
Some 'change' is fast and catastrophic, some is very slow and actually preserves artificially built structures.
There are also naturally occuring underwater structures that have carvings on them. That’s because somebody got around to whack away at them when the ocean level was lower. Anyone who gets stuck on the offshore “structure” in Souvrn’ Japan should take a good look at the Giants’ Causeway in Great Britain: http://www.google.com/search?q=giants+causeway&hl=en&prmd=ivnsm&tbm=isch&tbo=u&source=univ&sa=X&ei=FqKtTbeCEKjg0gGD-NWhCw&ved=0CCwQsAQ&biw=1333&bih=690
Essentially, that is what happened with the far northern and southern latitude landmasses covered with ice sheets two miles or more thick.
While there was some compression of the continental crust into the mantle by the sheer weight of the ice on the continents, (google: Isostacy and Isostatic rebound), the overall effect was a drop in sea level because that part of the hydrologic cycle had battlenecked. When the ice sheets melted off, the continents rebounded somewhat, rising relative to their former position floating on the mantle (still occurring according to some), but the ocean basin water levels rose faster, inundating the coastal areas which had been habitable while the ice sheets existed.